NE555 Monostable not turning off

Using Arduino General Electronics
1

This question is not specifically about Arduino, I am really sorry if that is a problem. However I am encountering an issue and I figured, there are quite a few smart people here.

I have an NE555 monostable circuit. I want to drive a 1.5W LED Strip, for that I have a 5V relay. The circuit works fine until I connect the relay to the output of the NE555. If I do that, the relay turns on on my button press, but not off anymore. I measured the voltage over the capacitor and it only rises until about 2/3 Vcc. It then fluctuates around that voltage.

I saw a previous similar post and a suggested issue was an insufficient power supply, however I think I can rule that out. If I don't connect the relay to pin3 of of the NE555 (The output pin), but leave it on the entire time so it draws the same amount of power, everything works fine as well. It is just if it is connected to pin3. Another hint suggestion that my issue is not the power supply is, that I can connect the led strip directly to the output pin. Then everything works fine, too. I don't want to do that, because the current it draws is much higher than what the Ne555 is rated for, I only did one test.

Summary: NE555 Monostable not turning off if relay connected to output pin, power supply not the issue.

The datasheet to my relay: https://www.circuitbasics.com/wp-content/uploads/2015/11/SRD-05VDC-SL-C-Datasheet.pdf

My circuit:

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rn_image_picker_lib_temp_bb226137-086e-4b6f-bd55-319a4b8c0dc63264×2448 285 KB

Thank you very much for your help in advance! I am still a beginner and the only other person who could help me is my dad, but this thing will be his Christmas present :smiley:. This also means I am very uncomfortable with transistors, main reason why I am using a relay.

This is my actual wiring with the components on the top drawn in. The white line is where the relay is supposed to go, the crossed out one was to test whether it was the voltage drop causing the problem.

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2

Give a link to the relay, what is written on it, what is its resistance ?

3

Here it is (also in the original post btw :slight_smile: )

4

The 555 will keep charging the timing cap as long as the trigger switch is closed. The trigger pulse must be shorter than the output pulse.

5

What is written on your relay ?

6

My trigger pulse is shorter than my output pulse. I aimed for a one minute output, and I only press the switch for a short amount of time.

7

Songle
10A 250VAC 10A 125VAC
10A 30VDC 10A 28VDC
SRD-05VDC-SL-C

This is all the text written on the relay other than a bit logo accompanying
I also measured a resistance of 66 Ohms

8

Hi,
is R1 = 560K?

9

This confirms 5v :+1:

Show us a good image of your ‘actual’ wiring.

When the relay is energized, measure the 5v supply ?

10

Yep

11

Hi,
Based on the monostable time formula with 555:

T = 1.1 * R * C.

T in seconds, R in Ohms, and C and Farady.

T = 1.1 * 560000 * 0.0001 = 61.1 Seconds.

For testing purposes replace the relay with an LED with a resistor.

1 Like
12

The supply drops down to about 4.9V. It all works fine tho if the relay is connected to plus directly instead of the NE's output. Then the voltage drop doesn't cause any issues. It is really just when it is connected to the output pin

13

Yeah, I will do that tomorrow and then test each component on it's own.

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