Garage door type switch...

[pebe]

Hi Adam. I had to read your reply several times to see what was happening. You mentioned holding L2 open, and that confused things for me. Also your line “Now, if I push the button while it is still traveling towards L1 it stops and if I push the button again it returns to L2” doesn’t make sense. If you press the button when it is traveling towards L1 it will not just stop – it will stop and immediately reverse.

Let us recap on how the circuit works. The 555 is basically a bistable latch. It has two states – a ‘set’ state where pin3 goes high, and a ‘reset’ state when pin3 goes low. Taking pin2 to a voltage below 1/3V (V=the supply voltage) will ‘set’ the output. Taking pin6 to a voltage higher then 2/3V will ‘reset’ the output. In this circuit, pins2&6 are tied together and held at 1/2 of the supply voltage, so the output is reset by taking both pins higher than 2/3V or set by taking the pins lower than 1/3V. When the pins return to the 1/2V level, the 555 will stay at the last commanded state.

The relay connected to pin3 will energise and run the motor one way when the 555 is set, and de-energise and reverse the motor when the 555 is reset. So the motor direction is dependent on the state of the 555 – not the limit switches. They are only there to limit the motor travel. Operation of the push button is like this. When the 555 is reset C2 discharges to 0V via R3. When the button is pressed, that 0V charge on C2 is impressed onto pins2/6. As pin2 goes below 1/3V that sets the 555 and pin3 goes high, energising the relay. With pin3 high, C2 will charge up via R3 to around 12V. So next time the button is pressed, pin6 goes high, resetting the 555. And so on ‘Ad Infinitum’.

From your description of events, the 555 is being reset in error. I don’t think it is the diode in backwards – that would cause it to blow. If it has blown it would be unlikely to give this problem because without it the 555 would falsely set – not reset.

My problem is that I am not there, meter in hand, to do a diagnosis – I can only react to tests that you do. So can I ask you to do a few more?
1. It is fairly obvious that pin6 is going above the 2/3V level in error. Would you check the voltage on that pin to be sure it is 1/2V. If it is not, R1 or R2 is the wrong value or the 555 is faulty.
2. Assuming that is correct then the likely problem is static from the mains wiring to the motor getting to pin6. Temporarily disconnect the motor. Now operate the push button several times (a few seconds apart) to ensure the relay goes on and off. If you cannot hear it clicking then measure pin3.
3. If all is OK so far then it is mains pickup on pin6. One of these should effect a cure:
a) Dress the mains wiring to the motor and limit switches away from the PC board.
b) Move the PCB as far away from the motor/wiring as possible.
c) Remove C1 from its present position on the PCB and wire it directly across pin 6 and pin8 of the 555 holder in order to keep the wiring to the cap as short as possible.

If it still malfunctions after these actions, will you let me know at what stage it goes wrong? Good luck!

[holbrooka]

I am very sorry!

I was quite unclear about the "button pushing" in the sentence:

"Now, if I push the button while it is still traveling towards L1 it stops and if I push the button again it returns to L2."

Here is what actually happened. When I pushed the momentary switch to start travel towards L1, things would work correctly, but only briefly, and the motor would change direction and travel back to L2 without any input. However, IF I manually activate (open) L1 during the brief period while it was working correctly, the motor would stop (as it would normally if it had reached L1). Then if I activated the momentary switch on again the unit would travel back up to L2 and stop once L2 was open.

I apologize for my poor description!

I will follow the rest of your testing instructions and get back to you!

I do know that the 555 works correctly and so does the relay DPDT switch. I have tested that numerous times prior to hooking up the AC and it shows correct continuity across terminals as expected. I am certain you are correct about something causing a surge at pin 6.... now to do all your troubleshooting ideas!

Thank you again for all of your help!

Adam

[holbrooka]

Okay... so the saga continues... BUT....

I ran through the tests, V=13.07, V6 was reading 6.5, all happy, V3 would fluctuate between 13 and 0 (or 1.3 sometimes)

I moved PCB as far from the AC wires and the motor as possible and...

The DPDT worked correctly under no load, but when AC applied it continued to malfunction!

So I moved C1 between pin 6 and 8 and it continued to malfunction.

So I went to replace the 555 chip and found that I had, at some point, bought a different chip so I had a choice of two....

I opted for the different one (
TI TLC555CP instead of the NE555P which I had used at least two of so far) AND.... (drum roll, please....)

It works! It goes up and stops when it hits the limit switch. When I push the Momentary on button, it reverses direction going down until it hits the lower limit switch and stops..... and it keeps doing it RIGHT every time I push the button!

I cannot thank you enough for your help and patience with me through all of this!!! I have had a great time, although slow, and learned a LOT more than I thought I would and I have a bunch of fun electrical parts to explore!

I can post a video of the thing, but I was concerned about the amount of bandwidth it would take up. If you would like to see it I will see what I can do.

Thank you again for all your help!!!!!! (I'm going to go push the button a few more times now!)

[pebe]

I'm pleased it's now working OK for you. I think the TI one is a CMOS version of the 555. That should not have made any difference.
I wonder if the NE555P had an internal leak between pins 3 and 6. That's about the only way I can account for your problem.