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# Help with ULN2003A motor driver

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#### loyaci

##### Newbie level 5
Hello friends...

i want to interface the ULN2003A with 12vdc stepper motor, i put a 5v in the inputs of the motor driver (5v for each in a sequence) but the output of the motor driver is low (0.6v) and cannot move the motor of course.
i change the ic and also increase the input voltage and still have the same problem

---------- Post added at 03:11 ---------- Previous post was at 03:08 ----------

this is the schematic for the circuit that i have done

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#### fumingsolder

##### Newbie level 3
Given that on your schematic the stepper only has 4 wires, I have to assume it's a bipolar one. These are a pain to drive with ULN2003 (or ULN2803 or other Darlington arrays) because the chips are designed to sink current and you need to be able to send both high and low voltages to each of the four wires.

You'd normally use H-bridge ICs to drive a bipolar stepper but if you are absolutely set on using ULN2003, you can float the wires off of a motor supply voltage on power resistors (and they will get really hot) and then sink with ULN if you need low voltage or let go if you need high. There is a schematic and Arduino code for just that here. The sample is based on ULN2803 but it's the same chip only 8 arrays rather than 7.

Good luck!

#### loyaci

##### Newbie level 5
i used a schemit trigger to convert the outputs of the uln2003a from low (0.6v) to high (5v) and then connect it to the motor and it works. i think i will need voltage regulator if i want to increase the voltage more.

thanks

#### Embedded_Geek

##### Full Member level 6
Remember that ULN2003 sinks current. Its not capable to source current...

umargill

Points: 2

umargill

### umargill

Points: 2

#### fumingsolder

##### Newbie level 3
i used a schemit trigger to convert the outputs of the uln2003a from low (0.6v) to high (5v) and then connect it to the motor and it works. i think i will need voltage regulator if i want to increase the voltage more.

thanks

Augmenting an ULN darlington array chip kinda defeats the purpose of using it.

At 60 cents per IC it's supposed to be a quick and cheap way of powering something that needs more sink than your logic (or MCU) can provide. If you find yourself needing to add more switches, you're much better off just abandoning the ULN idea and using a proper IC for what you're doing.

In this case a quad half-H-bridge IC such as SN754410 will do the job much nicer 'cause it'll both source and sink current (and more of it than UNL2003, too). It'll be something like 5 times more expensive but it''s still an under-$5 chip. Come to think of it, depending on the application you might as well look at an even higher specialized stepper motor driver chip such as Allegro 3967. It'll be a couple$ more expensive still but it will take just the step and direction signals and do microstepping on top of all its other goodness!

umargill

### umargill

Points: 2

#### loyaci

##### Newbie level 5
thank you friends,
i forget to tell, the motor is a unipolar stepper motor and it has 5 wires (4 phases and 1 GND). so which motor driver is the best? H-bridge IC (SN754410) or ULN's?

umargill

### umargill

Points: 2

#### ckshivaram

ULN 2803 is better compared to SN754410 series...........

umargill

### umargill

Points: 2

#### alexan_e

A unipolar motor can be driven fine using something like

ULN will work fine up to 500mA or you can use 2 outputs together for 1A.

Alex

umargill

### umargill

Points: 2

#### FvM

##### Super Moderator
Staff member
ULN will work fine up to 500mA or you can use 2 outputs together for 1A.
You should also consider the graph "Allowable output current as a function of duty cycle". For static load situations 1A is out of bounds.

umargill

### umargill

Points: 2

#### alexan_e

You should also consider the graph "Allowable output current as a function of duty cycle". For static load situations 1A is out of bounds.

Yes, you are correct, I should have checked the datasheet first.

Alex

umargill

### umargill

Points: 2

#### loyaci

##### Newbie level 5
i make the connection in the schematic and the motor works perfectly, this is really helpfull.
the problem that i put an LED in each output of the driver and when i take it off the motor works and drived very will by the ULN2003A

thank you

umargill

### umargill

Points: 2

#### alexan_e

If you want to use leds in the output of the ULN then you have to connect the led cathode to the ULN output (one led each output) and then the anode through a resistor for each led to the positive supply.

Alex

edit: since you feed the coil in parallel with the led it will probably not work because the coil has a much lower resistance.

Alex

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