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Topic: Problem with TIP120 transistor (Read 170 times) previous topic - next topic

Nocternity

Hello!

I'm trying to control a 12v solenoid lock (https://www.adafruit.com/product/1512) through a TIP120 with an Arduino, but can't get it to work. I've followed online guides and set it up as attached image, but when sending a digitalWrite(9, HIGH), nothing happens. If I connect the solenoid directly to the battery it works without problem.

The image shows a 9v battery due to lack of 12v variants in Fritzing, but I'm using a 12v 2.3A lead acid battery


MarkT

#1
Oct 27, 2019, 03:14 pm Last Edit: Oct 27, 2019, 03:16 pm by MarkT
Well the pinout is right, the circuit is right, perhaps double check every point in the circuit has the voltage you expect using a multimeter ?  A component might be faulty, or something is shorted out?

Have you tried shorting the negative wire of the solenoid to ground direct (bypassing the TIP120)?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Nocternity

#2
Oct 27, 2019, 08:13 pm Last Edit: Oct 27, 2019, 08:18 pm by Nocternity
Well the pinout is right, the circuit is right, perhaps double check every point in the circuit has the voltage you expect using a multimeter ?  A component might be faulty, or something is shorted out?

Have you tried shorting the negative wire of the solenoid to ground direct (bypassing the TIP120)?
I tried now to move down the negative wire from the solenoid to ground as you wrote (the black wire in my image down to where the other ground wires are connected), but nothing happens when I fed it with power. I assume the Arduino doesn't fill any purpose when bypassing the TIP120 and the solenoid should react directly when fed with power this way?

However, by connecting the negative of the solenoid to the base of the TIP120 and leave the collector "wireless" actually makes the solenoid react as expected, so I know it isn't broken (while I suppose doing it might've destroyed the TIP120).

I don't have access to a multimeter so I haven't been able to to try that though.

MarkT

Perhaps the Arduino pin is shorted to ground, or not working?  Does it control an LED/resistor combination?
BTW passing 0.5A through the base-emitter junction of the TIP120 might have damaged it, hope not.

You ought to get at least a cheap multimeter, its going to really help troubleshoot things like this.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Nocternity

Perhaps the Arduino pin is shorted to ground, or not working?  Does it control an LED/resistor combination?
BTW passing 0.5A through the base-emitter junction of the TIP120 might have damaged it, hope not.

You ought to get at least a cheap multimeter, its going to really help troubleshoot things like this.
I thought so too, that I've might've fried the TIP120, but replacing it with another one made no difference. I've also tried different pins on the Arduino and I also had a LED/resistor combination that ran at the same time on a different pin to make sure it was actually running the code, haha.. I did switch the jumper wires as well to make sure that the pin I used for the transistor was working

MarkT

Sure those TIP120's are kosher?  Many semiconductors from eBay are fake/junk/rejects/wrong.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Nocternity

Sure those TIP120's are kosher?  Many semiconductors from eBay are fake/junk/rejects/wrong.
I got these from a Swedish electronic store, but yeah it has crossed my mind that they might be faulty. I have two more to test + another Arduino, so I'm gonna give them a go as well and hope for the best. Can't for my life figure out what's wrong.

Nocternity

I solved it! or.. it works now. I removed everything and replaced it on a different breadboard, and that did it. Something (most likely the diode) wasn't probably securely connected.

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