Water Level Controller And Motor Protector

Many a time we forget to switch off the motor pushing water into the overhead tank (OHT) in our households. As a result, water keeps overflowing until we notice the overflow and switch the pump off
As the OHT is usually kept on the topmost floor, it is cumbersome to go up frequently to check the water level in the OHT.

Here’s a microcontroller-based water level controller-cum-motor protector to solve this problem. It controls ‘on’ and ‘off ’ conditions of the motor depending upon the level of water in the tank. The status is displayed on an LCD module. The circuit also protects the motor from high voltages, low voltages, fluctuations of mains power and dry running.

Circuit description

Fig. 1 shows the circuit of the microcontroller-based water level controller-cum-motor protector. It comprises operational amplifier LM324, microcontroller AT89C51, optocoupler PC817, regulator 7805, LCD module and a few discrete components. 
  
The AT89C51 (IC2) is an 8-bit microcontroller with four ports (32 I/O lines), two 16-bit timers/ counters, on-chip oscillator and clock circuitry. Eight pins of port-1 and three pins of port-3 are interfaced with data and control lines of the LCD module. Pins P3.0, P3.1 and P3.6 are connected to RS (pin 4), R/W (pin 5) and E (pin 6) of the LCD, respectively. Pin EA (pin 31) is strapped to V_cc for internal program executions. Switch S2 is used for backlight of the LCD module.
  
Power-on-reset is achieved by connecting capacitor C8 and resistor R14 to pin 9 of the microcontroller. Switch S1 is used for manual reset.
  
The microcontroller is operated with a 12MHz crystal. Port pins P2.0 through P2.2 are used to sense the water level, while pins P2.3 and P2.4 are used to sense the under-voltage and over-voltage, respectively. Pin P3.4 is used to control relay RL1 with the help of optocoupler IC3 and transistor T5 in the case of under-voltage, over-voltage and different water level conditions. Relay RL1 operates off a 12V supply. Using switch S3, you can manually switch on the motor.
The LM324 (IC1) is a quad operational amplifier (op-amp). Two of its op-amps are used as comparators to detect under- and over-voltage. In normal condition, output pin 7 of IC1 is low, making pin P2.3 of IC2 high. When the voltage at pin 6 of N1 goes below the set reference voltage at pin 5 (say, 170 volts), output pin 7 of N1 goes high. This high output makes pin P2.3 of IC2 low, which is sensed by the microcontroller and the LCD module shows ‘low voltage.’

In normal condition, pin 1 of N2 is high. When the voltage at pin 2 of N2 goes above the set voltage at pin 3, output pin 1 of N2 goes low. This low signal is sensed by the microcontroller and the LCD module shows ‘high voltage.’

Presets VR1 and VR2 are used for calibrating the circuit for under-and over-voltage, respectively.   
The AC mains is stepped down by transformer X1 to deliver a secondary output of 12V at 500 mA. The transformer output is rectified by a full-wave bridge rectifier comprising diodes D5 through D8, filtered by capacitor C2, and used for the under- and over-voltage detection circuitry.
  
The transformer output is also rectified by a full-wave bridge rectifier comprising diodes D1 through D4, filtered by capacitor C1 and regulated by IC4 to deliver regulated 5V for the circuit.
 
When water in the tank rises to come in contact with the sensor, the base of transistor BC548 goes high. This high signal drives transistor BC548 into saturation and its collector goes low. The low signal is sensed by port pins of microcontroller IC2 to detect empty tank, dry sump and full tank, respectively.
     
Operation

When water in the tank is below sensor A, the motor will switch on to fill water in the tank. The LCD module will show ‘motor on.’ The controller is programmed for a 10-minute time interval to check the dry-run condition of the motor. If water reaches sensor B within 10 minutes, the microcontroller comes out of the dry-run condition and allows the motor to keep pushing water in the tank.

The motor will remain ‘on’ until water reaches sensor C. Then it will stop automatically and the microcontroller will go into the standby mode. The LCD module will show ‘tank full’ followed by ‘standby mode’ after a few seconds. The ‘standby mode’ message is displayed until water in the tank goes below sensor A. 
  
In case water does not reach sensor B within 10 minutes, the microcontroller will go into the dry-running mode and stop the motor for 5 minutes, allowing it to cool down. The LCD module will show ‘dry-sump1.’
  
After five minutes, the microcontroller will again switch on the motor for
10 minutes and check the status at sensor B. If water is still below sensor B, it will go into the dry-running mode and the LCD module will show ‘dry-sump2.’
  
The same procedure will repeat, and if the dry-run condition still persists, the display will show ‘dry-sump3’ and the microcontroller will not start the motor automatically. Now you have to check the line for water and manually reset the microcontroller to start operation.
  
In the whole procedure, the microcontroller checks for high and low voltages. For example, when the voltage is high, it will scan for about two seconds to check whether it is a fluctuation. If the voltage remains high after two seconds, the microcontroller will halt running of the motor. Now it will wait for the voltage to settle down. After the voltage becomes normal, it will still check for 90 seconds whether the voltage is normal or not. After normal condition, it will go in the standby mode and start the aforementioned procedure.

Code:

$MOD51 START: LJMP MAIN_PGR ;GO TO MAIN PROGRAMME ORG 002FH MAIN_PGR: MOV A, # 38H ;INITIALIZE LCD LCALL WR_LCD MOV A, #0FH LCALL WR_LCD MOV A, #06H LCALL WR_LCD MOV A, #01H LCALL WR_LCD MOV A, #80H LCALL WR_LCD MOV A, #53H ;WRITE DATA TO LCD LCALL LCD_RAM ;i.e.,” STANDBY-MODE” MOV A, #54H LCALL LCD_RAM MOV A, #41H LCALL LCD_RAM MOV A, #4EH LCALL LCD_RAM MOV A, #44H LCALL LCD_RAM MOV A, #42H LCALL LCD_RAM MOV A, #59H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #0C0H ;JUMP TO 9TH POSITION LCALL WR_LCD ;OR SECOND LINE MOV A, #4DH ;ENTER DATA AGAIN LCALL LCD_RAM MOV A, #4FH LCALL LCD_RAM MOV A, #44H LCALL LCD_RAM MOV A, #45H LCALL LCD_RAM LJMP SCAN ;GO TO 010AH ORG 00A0H WR_LCD: LCALL SETT ;CHECK FOR READY STATUS OF LCD MOV P1,A ;MOVE CONTENTS OF A TO PORT 1 CLR P3.0 ;WRITE COMMANDS TO LCD CLR P3.1 SETB P3.6 CLR P3.6 RET ;RETURN TO PROGRAMME ORG 00C0H LCD_RAM: LCALL SETT ;CHECK READY STATUS OF LCD MOV P1,A ;MOVE CONTENS OF A TO PORT 1 SETB P3.0 ;WRITE TO DISPLAY RAM OF LCD CLR P3.1 SETB P3.6 CLR P3.6 RET ;GO TO PROGRAMME ORG 00F0H SETT: CLR P3.6 MOV P1, #0FFH ;SET PORT1 FOR INPUT NOP ;DELAY CLR P3.0 SETB P3.1 L1: CLR P3.6 SETB P3.6 JB P1.7,L1 ;IF NOT READY JUMP TO 00FA H CLR P3.6 RET ;BACK TO PROGRAMME ORG 010AH SCAN: SETB 76H ;SET USER FLAGS SETB 77H SETB 78H MOV P2,#0FFH ;SET PORT2 FOR INPUT L4: JNB P2.4,L2 ;IF H/V THEN GOTO 0136 H JNB P2.3,L3 ;IF L/V THEN GOTO 018B H JNB P2.0,L4 ;SCAN FOR TANK TO BE EMPTY SJMP L130 ;GOTO 0130 H LOOP: LCALL TMR_10MIN ;CALL 10 MIN. TIMER JNB 78H,L3 ;L/V THEN GOTO 018B H JNB 77H,L2 ;H/V THEN GOTO 0136 H JB 76H,L5 ;DRY SUMP THEN GOTO 0188 H JB P2.2,$ ;WAIT UNTILL TANK FULL LOOP1:LJMP TANK_FULL ;GOTO TANK FULL DISPLAY L130: CLR P3.4 ;START MOTOR LJMP DIS_M_ON ;DISPLAY MOTOR ON NOP ;BLANK SPACE L2: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.4,L4 ;STILL H/V THEN GOTO 0113 H LOOP2:SETB P3.4 ;H/V THEN OFF MOTOR NOP NOP LCALL INI_LCD ;INITIALIZE LCD MOV A, #48H ;DISPLAY HIGH-VOLTAGE LCALL LCD_RAM MOV A, #49H LCALL LCD_RAM MOV A, #47H LCALL LCD_RAM MOV A, #48H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #56H LCALL LCD_RAM MOV A, #4FH LCALL LCD_RAM MOV A, #04CH LCALL LCD_RAM MOV A, #0C0H ;MOVE TO 9TH CHARACTER LCALL WR_LCD MOV A, #54H LCALL LCD_RAM MOV A, #41H LCALL LCD_RAM MOV A, #47H LCALL LCD_RAM MOV A, #45H LCALL LCD_RAM LJMP CHK_HV ;GOTO 0490 H NOP ;BLANK SPACE L5: LJMP M_STOP ;GOTO 0226 H L3: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.3,L4 ;VOLTAGE OK THEN GOTO 0113 H LOOP3:SETB P3.4 ;STOP MOTOR IF ON LCALL INI_LCD ;INITIALIZE LCD MOV A, #04CH ;DISPLAY LOW-VOLTAGE LCALL LCD_RAM MOV A, #04FH LCALL LCD_RAM MOV A, #57H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #56H LCALL LCD_RAM MOV A, #04FH LCALL LCD_RAM MOV A, #04CH LCALL LCD_RAM MOV A, #54H LCALL LCD_RAM MOV A, #0C0H ;GOTO 9TH CHARACTER LCALL WR_LCD MOV A, #41H ;START DISPLAY AGAIN LCALL LCD_RAM MOV A, #47H LCALL LCD_RAM MOV A, #45H LCALL LCD_RAM LJMP CHK_LV ;GOTO 04B0 H NOP NOP NOP ORG 01D8H DLY_2SEC: MOV R3, #03H L8: MOV R4, #0FFH L7: MOV R5, #0FFH L6: NOP NOP NOP NOP NOP NOP DJNZ R5,L6 ;01DEH DJNZ R4,L7 ;01DCH DJNZ R3,L8 ;01DAH RET ;BACK TO PROGRAMME ORG 0226H M_STOP: SETB P3.4 ;STOP MOTOR LCALL INI_LCD ;INITIALIZE LCD MOV A, #44H ;START FILLING DISPLAY RAM OF LCD LCALL LCD_RAM MOV A, #52H LCALL LCD_RAM MOV A, #59H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #53H LCALL LCD_RAM MOV A, #055H LCALL LCD_RAM MOV A, #04DH LCALL LCD_RAM MOV A, #50H LCALL LCD_RAM MOV A, #0C0H ;MOVE TO 9TH CHARACTER OF LCD LCALL WR_LCD MOV A, #31H ;START WRITING AGAIN LCALL LCD_RAM LJMP L300 ;GOTO 0300 H TANK_FULL: SETB P3.4 ;STOP MOTOR NOP ;BLANK SPACES FOR FURTHER EXPANSION NOP NOP NOP NOP NOP NOP LCALL INI_LCD ;INITIALIZE LCD MOV A, #54H ;WRITE TO DISPLAY RAM OF LCD LCALL LCD_RAM MOV A, #41H LCALL LCD_RAM MOV A, #4EH LCALL LCD_RAM MOV A, #4BH LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #46H LCALL LCD_RAM MOV A, #55H LCALL LCD_RAM MOV A, #4CH LCALL LCD_RAM MOV A, #0C0H ;GOTO 9TH CHARACTER OF LCD LCALL WR_LCD MOV A, #4CH ;START DISPLAYING AGAIN LCALL LCD_RAM LCALL DLY_2SEC ;DISPLAY IT FOR 2 SECONDS LJMP START ;GOTO STANDBY MODE ORG 02B3H INI_LCD:MOV A, # 38H LCALL WR_LCD MOV A, #0FH LCALL WR_LCD MOV A, #06H LCALL WR_LCD MOV A, #01H LCALL WR_LCD MOV A, #80H LCALL WR_LCD RET ;BACK TO PROGRAMME NOP NOP NOP DIS_M_ON: LCALL INI_LCD ;INITIALIZE LCD MOV A, # 4DH ;WRITE INTO DISPLAY RAM OF LCD LCALL LCD_RAM MOV A, #04FH LCALL LCD_RAM MOV A, #54H LCALL LCD_RAM MOV A, #04FH LCALL LCD_RAM MOV A, #52H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #04FH LCALL LCD_RAM MOV A, #04EH LCALL LCD_RAM LJMP LOOP ;BACK TO MAIN PROGRAMME AT 011E H NOP NOP L300: LCALL TMR_5MIN ;CALL 5 MINUTES TIMER LJMP MAIN ;GOTO MAIN PROGRAMME AT 0550 H ORG 0320H TMR_5MIN: MOV R2,#03H L12: MOV R3, #0FFH L11: MOV R4, #0FFH L10: MOV R5, #0FFH L9: NOP NOP NOP NOP DJNZ R5, L9 ;0328 DJNZ R4, L10 ;0326 DJNZ R3, L11 ;0324 DJNZ R2, L12 ;0322 RET ;BACK TO MAIN PROGRAMME ORG 0430H L430: JNB P2.2,L43C ;IF TANK FULL GOTO 043C H JNB P2.4,L43F ;H/V THEN GOTO 043F H L436: JNB P2.3,L448 ;L/V THEN GOTO 0448 H L439: SJMP L430 ;GOTO 0430 H NOP L43C: LJMP LOOP1 ;ACK TO MAIN PROGRAMME L43F: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.4, L436 ;IF NOT H/V THEN GOTO 0436 H LJMP LOOP2 ;H/V THEN GOTO 013C H L448: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.3, L439 ;IF NOT L/V THEN GOTO 0439 H LJMP LOOP3 ;IF L/V THEN GOTO 0191 H ORG 0490H CHK_HV: NOP NOP L492: LCALL DLY_2MIN ;WAIT FOR 2 MINUTES JNB P2.4,L492 ;CHECK FOR H/V AGAIN LJMP START ;GOTO START AGAIN ORG 04B0H CHK_LV: NOP NOP L4B2: LCALL DLY_2MIN ;WAIT FOR 2 MINUTES JNB P2.3, L4B2 ;CHECK FOR L/V AGAIN LJMP START ;GOTO START AGAIN ORG 0500H DLY_2MIN: MOV R2, #0FFH L502: MOV R3,#0FFH L504: MOV R4,#0FFH L506: NOP NOP NOP NOP DJNZ R4, L506 DJNZ R3, L504 DJNZ R2, L502 RET ;BACK TO MAIN PROGRAMME ORG 054DH M_START: LJMP SUB_BR ;SUB BRANCH DUE TO SPACE PROBLEM MAIN: JNB P2.4, L59A ;CHECK FOR HIGH VOLTAGE JNB P2.3, L5A3 ;CHECK FOR LOW VOLTAGE CLR P3.4 ;IF VOLTAGE OK THEN START MOTOR LCALL INI_LCD ;INITIALIZE LCD MOV A, #04DH ;START WRITING TO DISPLAY RAM OF LCD LCALL LCD_RAM MOV A, #04FH LCALL LCD_RAM MOV A, #54H LCALL LCD_RAM MOV A, #4FH LCALL LCD_RAM MOV A, #52H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #4FH LCALL LCD_RAM MOV A, #4EH LCALL LCD_RAM LCALL TMR_10MIN ;ENTER INTO 10 MINUTES TIMER JNB 78H, C_LV; 05A9H ;LOW VOLTAGE THEN GOTO 05A9 H JNB 77H, C_HV; 05A0H ;HIGH VOLTAGE THEN GOTO 05A0 H JB 76H, DRY ;05ACH ;IF TANK DRY THEN GOTO 05AC H L58F: JNB P2.2, M_START ;TANK FULL THEN GOTO 054D H JNB P2.4, L59A ;HIGH VOLTAGE THENGOTO 059A H L595: JNB P2.3, L5A3 ;LOW VOLTAGE THEN GOTO 05A3 H L598: SJMP L58F ;REPEAT FROM 058F H L59A: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.4, L595 ;IF NOT H/V THEN GO BACK TO 0595 H C_HV: LJMP LOOP2 ;STILL H/V THEN GOTO 013C H L5A3: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.3, L598 ;IF NOT L/V THEN GO BACK TO 0598 H C_LV: LJMP LOOP3 ;STILL L/V THEN GOTO 0191 H DRY: SETB P3.4 ;STOP MOTOR LCALL INI_LCD ;INITIALIZE LCD MOV A, #44H ;START WRITING TO DISPLAY RAM OF LCD LCALL LCD_RAM MOV A, #52H LCALL LCD_RAM MOV A, #59H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #53H LCALL LCD_RAM MOV A, #55H LCALL LCD_RAM MOV A, #4DH LCALL LCD_RAM MOV A, #50H LCALL LCD_RAM MOV A, #0C0H ;GOTO 9TH CHARACTER OF LCD LCALL WR_LCD MOV A, #32H ;START WRITING AGAIN LCALL LCD_RAM LCALL TMR_5MIN ;WAIT FOR 5 MINUTES JNB P2.4,HV ; 0630H ;H/V THEN GOTO 0630 H JNB P2.3,LV ; 0639H ;L/V THEN GOTO 0639 H CLR P3.4 ;IF VOLTAGE OK THEN START MOTOR LCALL INI_LCD ;INITILIZE LCD MOV A, #4DH ;START WRITING TO DISPLAY RAM OF LCD LCALL LCD_RAM MOV A, #4FH LCALL LCD_RAM MOV A, #54H LCALL LCD_RAM MOV A, #4FH LCALL LCD_RAM MOV A, #52H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #4FH LCALL LCD_RAM MOV A, #4EH LCALL LCD_RAM LCALL TMR_10MIN ;GOTO MINUTES TIMER JNB 78H, L63F ;L/V THEN GOTO 063F H JNB 77H, L636 ;H/V THEN GOTO 0636 JB 76H, L647 ;STILL DRY SUMP THEN GOTO 0647 H L625: JNB P2.2, SUB_BR ;0642H ;TANK FULL THEN GOTO 0642 H JNB P2.4, HV ;0630H ;H/V THEN GOTO 0630 H N_HV: JNB P2.3, LV ;0639H ;L/V THEN GOTO 0639 H N_LV: SJMP L625 ;REPEAT FROM 0625 H HV: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.4, N_HV ;062BH ;IF NOT H/V THEN GOTO 062B H L636: LJMP LOOP2 ;STILL H/V THEN GOTO 013C H LV: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JB P2.3, N_LV ;062EH ;IF NOT L/V THEN GOTO 062E H L63F: LJMP LOOP3 ;STILL L/V THEN GOTO 0191 H SUB_BR: SETB P3.4 ;STOP MOTOR LJMP TANK_FULL ;TANK FULL THEN GOTO 0260 H L647: SETB P3.4 ;STOP MOTOR NOP NOP LCALL INI_LCD ;INITIALIZE LCD MOV A, #44H ;START WRITING TO DISPLAY RAM OF LCD LCALL LCD_RAM MOV A, #52H LCALL LCD_RAM MOV A, #59H LCALL LCD_RAM MOV A, #0B0H LCALL LCD_RAM MOV A, #53H LCALL LCD_RAM MOV A, #55H LCALL LCD_RAM MOV A, #4DH LCALL LCD_RAM MOV A, #50H LCALL LCD_RAM MOV A, #0C0H ;GOTO 9TH CHARACTER OF LCD LCALL WR_LCD MOV A, #33H ;START WRITING AGAIN LCALL LCD_RAM SJMP $ ;STAY HERE UNTILL MANUAL RESET ORG 0750H TMR_10MIN: MOV R2, #05H L752: MOV R3, #0FFH L754: MOV R4, #0FFH L756: MOV R5, #0FFH L758: NOP NOP NOP NOP NOP DJNZ R5, L758 DJNZ R4, L756 JNB P2.4,L770 ;H/V THEN GOTO 0670 H L764: JNB P2.3, L778 ;L/V THEN GOTO 0678 H L767: JNB P2.1, L780 ; NOT DRY SUMP THEN GOTO 0680 H L76A: DJNZ R3, L754 DJNZ R2, L752 RET ;BACK TO MAIN PROGRAMME NOP L770: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JNB P2.4, 0788H ;STILL H/V THEN GOTO 0788 H SJMP L764 ; NOT H/V THEN GOTO 0764 H L778: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JNB P2.3, 078BH ;STILL L/V THEN GOTO 078B H SJMP L767 ;NOT L/V THEN GOTO 0767 H L780: LCALL DLY_2SEC ;WAIT FOR 2 SECONDS JNB P2.1, 078EH ;STILL NOT DRY SUMP THEN GOTO 078E H SJMP L76A ;OTHERWISE GOTO 076A CLR 77H ;CLEAR FLAG 77H FOR H/V RET CLR 78H ;CLEAR FLAG 78H FOR L/V RET CLR 76H ;CLEAR FLAG 76H FOR DRY SUMP CHECK RET END

Microcontroller Based Solar Charger

As the sources of conventional energy deplete day by day, resorting to alternative sources of energy like solar and wind energy has become need of the hour.

Solar-powered lighting systems are already available in rural as well as urban areas. These include solar lanterns, solar home lighting systems, solar streetlights, solar garden lights and solar power packs. All of them consist of four components: solar photovoltaic module, rechargeable battery, solar charge controller and load.

In the solar-powered lighting system, the solar charge controller plays an important role as the system’s overall success depends mainly on it. It is considered as an indispensable link between the solar panel, battery and load.

The microcontroller-based solar charge controller described here has the following features:

1. Automatic dusk-to-dawn operation of the load
2. Built-in digital voltmeter (0V-20V range)
3. Parallel- or shunt-type regulation
4. Overcharge protection
5. System status display on LCD
6. Deep-discharge protection
7. Low battery lock
8. Charging current changes to ‘pulsed’ at full charge
9. Low current consumption
10. Highly efficient design based on microcontroller
11. Suitable for 10-40W solar panels for 10A load

The circuit of the solar charge controller is shown in Fig. 1. It comprises microcontroller AT89C2051, serial analogue-to-digital converter ADC0831, optocoupler MCT2E, regulator 7805, MOSFETs BS170 and IRF540N, transistor BC547, LCD and a few discrete components. Component description is given below.

Microcontroller. Microcontroller AT89C2051 is the heart of the circuit. It is a low-voltage, high-performance, 8-bit microcontroller that features 2 kB of Flash, 128 bytes of RAM, 15 input/output (I/O) lines, two 16-bit timers/counters, a five-vector two-level interrupt architecture, a full-duplex serial port, a precision analogue comparator, on-chip oscillator and clock circuitry. A 12MHz crystal is used for providing the basic clock frequency. All I/O pins are reset to ‘1’ as soon as RST pin goes high. Holding RST pin high for two machine cycles, while the oscillator is running, resets the device. Power-on reset is derived from resistor R1 and capacitor C4. Switch S2 is used for manual reset.
   
Serial ADC.  The microcontroller monitors the battery voltage with the help of an analogue-to-digital converter. The ADC0831 is an 8-bit successive approximation analogue-to-digital converter with a serial I/O and very low conversion time of typically 32 μs. The differential analogue voltage input allows increase of thecommon-mode rejection and offsetting of the analogue zero input voltage. Inaddition, the voltage reference input can be adjusted to allow encoding of anysmaller analogue voltage span to the full eight bits of resolution. It is available in an 8-pin PDIP package and can be interfaced to the microcontroller with only three wires.
   
LCD module. The system status and battery voltage are displayed on an LCD based on HD44780 controller. The backlight feature of the LCD makes it readable even in low light conditions. The LCD is used here in 4-bit mode to save the microcontroller’s port pins. Usually the 8-bit mode of interfacing with a microcontroller requires eleven pins, but in 4-bit mode the LCD can be interfaced to the microcontroller using only seven pins.
   
Solar panel. The solar panel used here is meant to charge a 12V battery and the wattage can range from 10 to 40 watts. The peak unloaded voltage output of the solar panel will be around 19 volts. Higher-wattage panels can be used with some modifications to the controller unit.
   
Rechargeable battery. The solar energy is converted into electrical energy and stored in a 12V lead-acid battery. The ampere-hour capacity ranges from 5 Ah to 100 Ah.
   
Dusk-to-dawn sensor. Normally, in a solar-photovoltaic-based installation—for example, solar home lighting system, solar lantern or solar streetlight—the load (the light) is switched on at dusk (evening) and switched off at dawn (morning). During daytime, the load is disconnected from the battery and the battery is recharged with current from the solar panel. The microcontroller needs to know the presence of the solar panel voltage to decide whether the load is to be connected to or disconnected from the battery, or whether the battery should be in charging mode or discharging mode. A simple sensor circuit is built using a potential divider formed around resistors R8 and R9, zener diode ZD1 and transistor T1 for the presence of panel voltage.
   
Charge control. Relay RL1 connects the solar panel to the battery through diode D1. Under normal conditions, it allows the charging current from the panel to flow into the battery. When the battery is at full charge (14.0V), the charging current becomes ‘pulsed.’ To keep the overall current consumption of the solar controller low, normally-closed (N/C) contacts of the relay are used and the relay is normally in de-energised state.
   
Load control. One terminal of the load is connected to the battery through fuse F1 and another terminal of the load to an n-channel power MOSFET T3. MOFETs are voltage-driven devices that require virtually no drive current. The load current should be limited to 10A. One additional MOSFET is connected in parallel for more than 10A load current.

Circuit description

Basically, there are two methods of controlling the charging current: series regulation and parallel (shunt) regulation. A series regulator is inserted between the solar panel and the battery. The series type of regulation ‘wastes’ a lot of energy while charging the battery as the control circuitry is always active and series regulator requires the input voltage to be 3-4 volts higher than the output voltage. The current and voltage output of a solar panel is governed by the angle of incidence of light, which keeps varying.
   
Parallel regulation is preferred in solar field. In parallel regulation, the control circuitry allows the charging current (even in mA) to flow into the battery and stop charging once the battery is fully charged. At this stage, the charging current is wasted by converting into heat (current is passed through low-value, high-wattage resistor); this part of the regulation dissipates a lot of heat.
   
In this project, we have used parallel regulation technique but instead of wasting the charging current as heat, we have made it pulsed and applied to the battery to keep the battery topped-up.
   
After power-on, the microcontroller reads the battery voltage with the help of the ADC and displays the values on the LCD. It monitors the input signal from the dusk-to-dawn sensor and activates the load or charging relay RL1 accordingly. The digital voltmeter works up to 20V. As V_ref of the ADC is connected to V_CC (5V), the input voltage to the ADC cannot exceed +5V. A potential divider is used at pin 2 of the ADC (IC2) using resistors R5, R6 and R7 to scale down the voltage from 0V-20V to 0V-05V. The ADC output is multiplied four times and displayed on the LCD as battery voltage.
   
When the solar panel voltage is present, the dusk-to-dawn sensor provides a signal to the microcontroller, which then displays ‘charging’ message on the LCD. During charging, the battery voltage is continuously monitored. When the voltage reaches 14.0V, the microcontroller interrupts the charging current by energising the relay, which is connected to MOSFET BS170 (T2), and starts a 5-minute timer. During this stage, the LCD shows “battery full.”
   
After five minutes, the relay reconnects the panel to the battery. This way, the charging current is pulsed at the intervals of five minutes and the cycle repeats until the panel voltage is present.
   
When the panel voltage falls below the zener diode (ZD1) voltage of the dusk-to-dawn sensor, the microcontroller senses this and activates the load by switching on MOSFET T3 via optocoupler IC3 and “load on” message is displayed.
   
In this mode, the microcontroller monitors for low battery. When the battery voltage drops below 10 volts, the microcontroller turns off the load by switching off MOSFET T3 and “battery low—load off” message is displayed.

Normally, when the load is switched off, the battery voltage tends to rise back and the load oscillates between ‘on’ and ‘off ’ states. To avoid this, the microcontroller employs a hysteresis control by entering into a ‘lock’ mode during low-battery state and comes out of the lock mode when the dusk-to-dawn sensor receives the panel voltage (the next morning). During lock mode, the microcontroller keeps converting the ADC value and displays the battery voltage on the LCD.

Code:

;************************************************************************************** ; SOLAR CHARGE CONTROLLER WITH DIGITAL VOLTMETER-ADC0831+LCD+8051 ;************************************************************************************** $MOD51 ; LCD 4-BIT MODE CONNECTIONS RS EQU P1.7 ;LCD REGISTER SELECT LINE EN EQU P1.6 ;LCD ENABLE LINE DB4 EQU P1.5 ; DB5 EQU P1.4 ; DB6 EQU P1.3 ; DB7 EQU P1.2 ; ; ADC0831 CONNECTIONS CS EQU P3.0 CLK EQU P3.1 DO EQU P3.2 ;INPUT & OUTPUT DYI EQU P3.4 ; SOLAR PANEL VOLTAGE SENSOR CHG_RL EQU P3.5 ; CHARGING CONTROL RELAY LD_RL EQU P3.7 ; LOAD CONTROL RELAY DSEG ORG 0020H VAL1: DS 1 VAL2: DS 1 VAL3: DS 1 ADC_VAL: DS 1 BUF: DS 1 CNT1: DS 1 CNT2: DS 1 IMG: DS 1 FLAGS: DS 1 OCF BIT FLAGS.0 ; OVER CHARGE FLAG LBF BIT FLAGS.1 ; LOW BATT FLAG CSEG ORG 0000H JMP MAIN ORG 000BH ;Timer Interrupt0 JMP COUNTDOWN MAIN: MOV SP,#50H MOV P3,#0FFH MOV P1,#0FFH CLR CHG_RL CLR LD_RL LCALL PWR_DELAY LCALL INIT SETB CLK SETB DO SETB CS SETB DYI MOV VAL1,#00H MOV VAL2,#00H MOV VAL3,#00H MOV FLAGS,#00H LOADCHAR: MOV BUF,#40H LCALL CMD MOV DPTR,#RCHAR REP: CLR A MOVC A,@A+DPTR JZ SCREEN1 MOV BUF,A LCALL DAT INC DPTR SJMP REP SCREEN1: MOV BUF,#80H LCALL CMD MOV DPTR,#MSG1 HERE: CLR A MOVC A,@A+DPTR JZ NEXT MOV BUF,A LCALL DAT INC DPTR SJMP HERE NEXT: MOV BUF,#0C0H LCALL CMD MOV DPTR,#MSG2 HERE1: CLR A MOVC A,@A+DPTR JZ OVER MOV BUF,A LCALL DAT INC DPTR SJMP HERE1 OVER: LCALL ONE_SEC_DELAY LCALL ONE_SEC_DELAY LCALL CLEAR MOV BUF,#0C0H LCALL CMD MOV DPTR,#MSG7 HERE2:CLR A MOVC A,@A+DPTR JZ CONVERT MOV BUF,A LCALL DAT INC DPTR SJMP HERE2 CONVERT: LCALL DDELAY CLR CS ; INITIATE CONVERSION SETB CLK CLR CLK ; FIRST CLOCK SETB CLK CLR CLK ; SECOND CLOCK MOV A,#00H ; CLEAR A MOV R5,#08H ; 8 CLOCK PULSES AGAIN: MOV C,DO RLC A SETB CLK CLR CLK DJNZ R5,AGAIN SETB CS MOV ADC_VAL,A MOV B,#79D MUL AB ; PRODUCT IN AB MOV R1,B ; HIGH BYTE IN B MOV R2,A ; LOW BYTE IN A LCALL HEX2BCD MOV VAL1,R7 MOV VAL2,R6 MOV VAL3,R5 LCALL SENDVAL2LCD CHECK: JNB LBF,CHECK2 ; SEE IF ANY FLAGS ARE SET ,i,e LOW BATT FLAG OR BATT FULL FLAG JB DYI,CONVERT CHECK2:JNB OCF,PROCEED JB DYI,NIGHT SJMP CONVERT PROCEED:JB DYI,NIGHT CLR LD_RL ; OFF LOAD CLR LBF ; CLEAR LOW BATT FLAG MOV A,VAL2 ; SEE IF BATT.IS FULL XRL A,#04H JZ FULLCHG CLR CHG_RL ; CONNECT BATT. TO PANEL MOV DPTR,#MSG4 ; DISPLAY CHARGING MSG MOV IMG,#00H LCALL SENDSTAT2LCD LJMP CONVERT FULLCHG: SETB OCF ;SET OVERCHARGE FLAG SETB CHG_RL ;DISCONNECT BATT.FROM PANEL MOV TH0,#03CH ;START 5 MIN TIMER HERE MOV TL0,#0B0H ;DISCONNECT BATT FROM PANEL MOV CNT1,#200D MOV CNT2,#30D SETB ET0 SETB TR0 SETB EA MOV DPTR,#MSG5 ; DISPLAY BATT.FULL MSG MOV IMG,#01H LCALL SENDSTAT2LCD LJMP CONVERT NIGHT: CLR CHG_RL ; RECONNECT BATT. TO PANEL CLR TR0 ; STOP TIMER0 INCASE ITS RUNNING CLR OCF ; CLEAR OVER CHARGE FLAG SETB LD_RL ; CONNECT LOAD TO BATT. MOV A,VAL1 XRL A,#00H JZ LOWBAT MOV DPTR,#MSG3 ; DISPLAY LOAD ON MSG MOV IMG,#02H LCALL SENDSTAT2LCD LJMP CONVERT LOWBAT: SETB LBF CLR LD_RL ; DISCONNECT LOAD FROM BATT. MOV DPTR,#MSG6 ; DISPLAY BAT.OW AND LOAD OFF MSG MOV IMG,#03H LCALL SENDSTAT2LCD LJMP CONVERT ;****************************************************************************** SENDVAL2LCD: MOV BUF,#0C7H LCALL CMD MOV A,VAL1 ORL A,#30H MOV BUF,A LCALL DAT MOV A,VAL2 ORL A,#30H MOV BUF,A LCALL DAT MOV BUF,#'.' LCALL DAT MOV A,VAL3 ORL A,#30H MOV BUF,A LCALL DAT RET ;****************************************************************************** SENDSTAT2LCD: MOV BUF,#080H LCALL CMD HERE3: CLR A MOVC A,@A+DPTR JZ PICT MOV BUF,A LCALL DAT INC DPTR SJMP HERE3 PICT: MOV BUF,#0CEH LCALL CMD MOV BUF,IMG LCALL DAT BACK: RET ;****************************************************************************** ; TIMER0 ISR (5 MINUTES TIMER) ;****************************************************************************** COUNTDOWN: CLR TR0 MOV TH0,#03CH MOV TL0,#0B0H SETB TR0 DJNZ CNT1,BACK2 MOV CNT1,#200D DJNZ CNT2,BACK2 CLR TR0 ; OFF 5 MIN TIMER CLR ET0 CLR OCF ; CLEAR OVER CHARGE FLAG CLR CHG_RL ; RE-CONNECT BATT TO PANEL BACK2: RETI ;****************************************************************************** Hex2BCD: MOV R3,#00D MOV R4,#00D MOV R5,#00D MOV R6,#00D MOV R7,#00D ACALL H2B RET H2B: MOV B,#10D MOV A,R2 DIV AB MOV R3,B ; MOV B,#10 ; R7,R6,R5,R4,R3 DIV AB MOV R4,B MOV R5,A CJNE R1,#00H,HIGH_BYTE ; CHECK FOR HIGH BYTE SJMP ENDD HIGH_BYTE: MOV A,#6 ADD A,R3 MOV B,#10 DIV AB MOV R3,B ADD A,#5 ADD A,R4 MOV B,#10 DIV AB MOV R4,B ADD A,#2 ADD A,R5 MOV B,#10 DIV AB MOV R5,B CJNE R6,#00D,ADD_IT SJMP CONTINUE ADD_IT: ADD A,R6 CONTINUE: MOV R6,A DJNZ R1,HIGH_BYTE MOV B, #10D MOV A,R6 DIV AB MOV R6,B MOV R7,A ENDD: RET ;************************************************************************************ ONE_SEC_DELAY: MOV R0,#10D ; One second delay routine RZ3: MOV R1,#100D RZ1: MOV R2,#250D RZ2: NOP NOP DJNZ R2,RZ2 DJNZ R1,RZ1 DJNZ R0,RZ3 RET ;************************************************************************************ PWR_DELAY: ; 15 mSec DELAY FOR LCD TO INTIALIZE AFTER POWER-ON MOV R4,#100D H2: MOV R3,#250D H1: DJNZ R3,H1 DJNZ R4,H2 RET ;********************LCD SUBROUTINES************************************** CMD: PUSH ACC ; SAVE ACCUMULATOR SETB EN CLR RS ; SELECT SEND COMMAND MOV A,BUF ; PUT DATA BYTE IN ACC MOV C, ACC.4 ; LOAD HIGH NIBBLE ON DATA BUS MOV DB4,C ; ONE BIT AT A TIME USING... MOV C, ACC.5 ; BIT MOVE OPERATOINS MOV DB5,C MOV C, ACC.6 MOV DB6,C MOV C, ACC.7 MOV DB7,C CLR EN NOP SETB EN ; PULSE THE ENABLE LINE MOV C, ACC.0 ; SIMILARLY, LOAD LOW NIBBLE MOV DB4,C MOV C, ACC.1 MOV DB5,C MOV C, ACC.2 MOV DB6,C MOV C, ACC.3 MOV DB7,C CLR EN NOP SETB EN ; PULSE THE ENABLE LINE LCALL MSDELAY POP ACC RET ; ********************LCD SUBROUTINES************************************** DAT: PUSH ACC ; SAVE ACCUMULATOR SETB EN SETB RS ; SELECT SEND DATA MOV A, BUF ; PUT DATA BYTE IN ACC MOV C, ACC.4 ; LOAD HIGH NIBBLE ON DATA BUS MOV DB4,C ; ONE BIT AT A TIME USING... MOV C, ACC.5 ; BIT MOVE OPERATOINS MOV DB5,C MOV C, ACC.6 MOV DB6,C MOV C, ACC.7 MOV DB7,C CLR EN NOP SETB EN ; PULSE THE ENABLE LINE MOV C, ACC.0 ; SIMILARLY, LOAD LOW NIBBLE MOV DB4,C MOV C, ACC.1 MOV DB5,C MOV C, ACC.2 MOV DB6,C MOV C, ACC.3 MOV DB7,C CLR EN NOP SETB EN ; PULSE THE ENABLE LINENOP LCALL MSDELAY POP ACC RET ;********************LCD SUBROUTINES************************************** CLEAR: MOV BUF,#01H LCALL CMD RET ;****************************LCD SUBROUTINES**************************************** DDELAY: MOV R5,#41D ; 4.1 mS DELAY QT2: MOV R6,#50D QT1: DJNZ R6,QT1 DJNZ R5,QT2 RET ;****************************LCD SUBROUTINES**************************************** MSDELAY: MOV R5,#26D QT22: MOV R6,#50D QT11: DJNZ R6,QT11 DJNZ R5,QT22 RET ;****************************LCD SUBROUTINES**************************************** INIT: MOV BUF,#30H ; FUNCTION SET - DATA BITS, LINES, FONTS LCALL CMD ACALL DDELAY ;INITIAL DELAY 4.1MSEC MOV BUF,#30H ; FUNCTION SET - DATA BITS, LINES, FONTS LCALL CMD ACALL DDELAY ;INITIAL DELAY 4.1MSEC MOV BUF,#30H ; FUNCTION SET - DATA BITS, LINES, FONTS LCALL CMD ACALL DDELAY ;INITIAL DELAY 4.1MSEC MOV BUF,#28H ;2 LINES 5X7, 4-BIT MODE LCALL CMD MOV BUF,#0CH ; DISPLAY ON LCALL CMD MOV BUF,#01H ; CLEAR DISPLAY, HOME CURSOR LCALL CMD MOV BUF,#06H ; SET ENTRY MODE LCALL CMD ; INCREMENT CURSOR RIGHT, NO SHIFT RET ;************************************************************************************ ORG 0320H MSG1: DB ' SOLAR CHARGE ',00H MSG2: DB ' CONTROLLER-EFY ',00H MSG3: DB ' LOAD ON ',00H MSG4: DB ' CHARGING ',00H MSG5: DB ' BATTERY FULL ',00H MSG6: DB 'BAT.LOW-LOAD OFF',00H MSG7: DB 'Volts: ',00H ORG 0400H RCHAR: DB 04D,31D,17D,31D,17D,31D,17D,31D ; CHARGING DB 04D,31D,31D,31D,31D,31D,31D,31D ; FULL DB 31D,31D,14D,04D,04D,14D,31D,31D ; LOAD DB 04D,31D,17D,17D,17D,17D,17D,31D ; LOW BATT DB 31D,31D,31D,31D,31D,31D,31D,31D DB 31D,31D,31D,31D,31D,31D,31D,31D DB 31D,31D,31D,31D,31D,31D,31D,31D DB 031D,31D,31D,31D,31D,31D,31D,31D,00H END

Crystal Tester With BC547

Here is a simple circuit that can be used to test a crystal before using it in a circuit. The circuit is built around two BC547 transistors (T1 and T2) and a few discrete components. 

 The oscillator circuit formed by transistor T1, resistors R1 and R2, and capacitors C1 and C2 oscillates if a good crystal is connected to the test points marked as CUT (crystal under test). The output from the oscillator is rectified by diode D1 and filtered by capacitor C3. The positive voltage appearing across the capacitor is fed to the base of transistor T2, causing it to conduct.

Testing of a crystal is simple: Insert the crystal at CUT points shown in the circuit diagram and press test switch S1. If LED1 glows, your crystal is good and you can use it in a circuit.

The circuit is powered by a standard 9V battery. Push-to-on switch S1 is included to prolong the battery life but it’s not needed if you use a socket for the crystal under test.

Assemble the circuit on a general-purpose PCB and enclose in a suitable small cabinet. Fix the two-pin connector, LED1 and test switch on top of the cabinet. Fix the 9V battery inside the cabinet.

Note. You can use 2N3563 transistors instead of BC547.