Cytron Technical Forum

Hello Guys,

I know that this miniature 3V DC motor need minimum 270mA @ 3.3V which is direct PIC output pin cannot supply that high current need. That’s why I use ULN2003 to drive up current from PIC to higher current then activate the 5V SPDT relay to throw the contactor to the other 5V side. (see photo)
Connection seems OK.

I try direct connecting motor to VDD & VSS of PIC and the motor is running. Just want to make sure motor is OK.
Then I put simple program code (ON RD0 continuously all times) – I want to confirm the current from output pin RD0 is not sufficient. And yes, motor is not running, but if put LED it will light up all times. Very true, I need to use ULN2003 to drive the motor.

I look everywhere (datasheet, google other blogs) but they were all the same connection to use ULN2003. I followed the connection. But the relay is not ‘clicking’ to show it is energized.

I again direct connect motor to output pin 16 of ULN2003 which is supposed to be output for pin 1 input. No response to the motor. I suspect the ULN2003 is not working.
Relay is working fine. I have tested the relay alone with 0V and 5V at 270mA & 100mA to both coils without problem.

Thanks.

Hi, I think something wrong with your circuit. You need to place pull up resistor between output and COM pin at ULN2003. Hope it may help.

Hi mohdismiaswaly, it looks like your circuit is wrong but I can't see the pin connection clearly, so could you post your schematic diagram here? Thanks.

Hi,

Take note that output from ULN2003 chip gives LOW output when input is HIGH. Therefore I think may be there are some modification you need to make for your circuit connection. Hope it helps!

Hello Guys,

I have again tested the chip, but now I put LED blinking program code to test chip functionality.
Pin 8 to VSS & Pin 9 to VDD of PIC. RD1 go to Pin 1.

Also, have pull-up resistor of 220Ohm (more brighter LED), previously tested with 4.7kOhm but not as bright as 220Ohm.

So it is working to blink the LED I checked voltage across the LED only 2.2V.

However, after I remove the LED, now jump to relay coil (one side of the coil to pin 16 of the chip & the other side to GND of PIC), the relay not working (no clicking sounds). Seems the voltage from pin 16 is too low? My relay is 5V.

If I test relay coil with direct 5V regulated power supply, it is OK, with clicking sound.

Help anyone?

Hi,

Yes it might be caused by insufficient voltage across relay (or insufficient current) due to the 220 ohm resistor. Why don't you try turn another way around? One coil of relay is connected to pin 16 of the chip, and another coil is connected directly to 5V? So that if input to the chip is HIGH, output is LOW and it will activate the relay. When the input is low, output will be open-circuit and 'deactivate' relay.

Hope it helps.

PS: 220ohm resistor is not needed in this case.

Hi mohdismiaswaly, I have google "ULN2003 + relay, interface with microcontroller" and found this schematic. You can try it.


Thanks.