inexpensive timing relay circuit

Thread Starter

strpdbas

Joined Dec 24, 2008
99
I had already redesigned the board from orig. 3" x 4" to have more room in enclosure for limit switches. Now all components fit on 3" x 3" board. This also gives me 16 boards instead of 12 from 12"sq. presensitized board. I am going to use original board but would like to ensure I correctly included the new components.
 

Thread Starter

strpdbas

Joined Dec 24, 2008
99
I built another unit and I guess I followed your direction correctly. It works fine. I wish to thank you again for all of your help and patience. I ask only for one more piece of information. Can you give me a list of voltage tests I can perform at each of the critical components to ensure all is working properly?
 

eblc1388

Joined Nov 28, 2008
1,542
Sorry strpdbas for late reply as I'm on a long vacation and still is.
I'll back sometimes in the week after April.

I hope your project is working well.
 

Thread Starter

strpdbas

Joined Dec 24, 2008
99
Thanks for getting back to me. I thought you might be away. So far all seems to be working correctly. The prototype is completed! Contact me when you return. I hope you are enjoying your holiday.
Strpdbas
 

Thread Starter

strpdbas

Joined Dec 24, 2008
99
I know you are still away, but since getting the prototype completed I would appreciate a review of my "final" board layout. I would also appreciate a procedure to troubleshoot malfunctions. I understand the operation of the circuit but need to be able to diagnose any problems I might encounter. For instance, I built 4 boards without incident but the last one is giving me timing problems. The reversal works but the time delay is not working properly. Adjusting the vr has little effect on the delay. A test procedure would allow me to isolate any possible problems, rather than arbitrarily changing components. I spent a fair amount of time reviewing how the ic's function but none were in layman's terms. Your review of the final circuit will ensure I put everything where it belongs
View attachment board.pdf.
 

eblc1388

Joined Nov 28, 2008
1,542
Your new board design does not have a continuous ground loop around your low voltage circuit element. A jumper on the other side does not function to close the loop and will not work.

I have made corrections to the board design so now all low voltage parts are on the "other side" of the ground loop and will be protected against leakage from the high AC line voltage. Now you have only one jumper on the board.

I noticed that you have chosen to use the 2N2222B transistor instead for the 555 and have a 2K2 base resistor to 0V. I now consider it better to use a higher value resistor like 10K ~ 22K for the base resistor to 0V. This will give a more robust operation regarding triggering.

The easiest method of troubleshooting is to keep a working one as a reference. Then if another circuit board don't work OK, one can check for problem using a ohmmeter only.

Power down the problematic board and join its 0V point with that of the good board, using a piece of short wire or a clip. Then connect a ohmmeter meter black lead to the 0V and use the red meter lead to poke around the same point on both circuits. A difference of resistance reading would usually indicate where the problem is. Look at the circuit diagram around that point and poke further until you have located the defect. This method is also very useful to detect minor cracks on the PCB too.

Try and see what comes up using this method. I will write up a short functioning description of the circuit or you later.

 

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Thread Starter

strpdbas

Joined Dec 24, 2008
99
Thanks for the correction of ground trace.
Two ?,s; the transistor is to be a 2N2222"A" as on your last ckt. mod or "B" as above?
Also to be clear I should now have two 10K resistors? One for the change from 2N7000 to 2N2222 and you now suggest changing R2 - from 2K2 to 10K as well?
 

eblc1388

Joined Nov 28, 2008
1,542
the transistor is to be a 2N2222"A" as on your last ckt. mod or "B" as above?
The "A" or "B" suffix means the different gains of the same transistor. The gain does not matter in your aplication so 2N2222, 2N2222A or 2N2222B will do.

Also to be clear I should now have two 10K resistors? One for the change from 2N7000 to 2N2222 and you now suggest changing R2 - from 2K2 to 10K as well?
Yes.
 

Thread Starter

strpdbas

Joined Dec 24, 2008
99
I hope you have returned from your holiday. I was hoping you could prepare a troubleshooting guide for me. I realize a lot of the information is spread out among the posts and replies but I am constantly scrolling to find the answer I need each time I encounter a problem. I thought all was under control with the new board layout but I am now experiencing instant motor reversal when pressing a limit switch. I would like to be able to quickly identify where to look and what measurements to take to isolate a particular problem. I also posted a question to get some help properly identifying how the leads of the 2n7000 compare to the 2n2222a.


View attachment 8938
 

eblc1388

Joined Nov 28, 2008
1,542
I hope you have returned from your holiday. I was hoping you could prepare a troubleshooting guide for me.
Yes I'm back.

As promised, the troubleshooting guide, Version #1a.

I would suggest you perform the following checks on every board you have built because the test is so easily to carry out which takes only a few minutes.



Circuit Checking Procedure
==========================

* All following checks use voltmeter, with black lead always connected to 0V. High=12V, Low=0V.
* One needs to be careful with diode polarity/direction. Wrong diode direction across relay will kill other component
* The following assume component polarity/direction are correct.
* light toggle means changing from one lamp into another

1. Do not connect motor yet but use two lamps instead

2. Power up, confirm 12V on check point A and B

3. Adjust timing R3 100K VR to min.

4. monitor point E voltage

5. Press limit switch one after another, point E should toggle(from high to low or low to high), you should see lamp go off and then changes from one to another too

5a. if everything is as expected so far, board is fine. Goto step 15.

6. If point E toggles but lights don't(i.e. just goes off & then SAME light On), check R4 1M for open circuit, shorted C1, bad 2N7000 or bad relay

6a. If point E toggles but lights toggle immediately without going off first, goto step 9

7. If point E voltage not changing then check point C & D. They should change when corresponding limit switch is pressed

8. If C & D not correct then bad limit switch. If correct, 4013 bad, switch power off and replace. Go to step 4

9. Confirm point F voltage changes from 12V to near 0V with pressing of either limit switch

10. If point F not changing, check for bad D1/D2, the two 10K resistors, 2N7000 or 2n2222

11. If point F changing but lamp not go off, checks point G.

12. If point G goes high when limit switch press but lamp not go off then bad relay.

12a. If point G goes high and does not returns to LOW(the lamp stays OFF) and 555's pin#6 voltage stays below 4V all the time then there is problem with the timing component. Check VR, 1K & 22K resistors and 100uF timing capacitor around pin#6.

13. If point G dead(stays LOW) then replace 555. Goto step 11

14. the circuit should work fine at this point

15. set VR to max. and check timing. set VR to desired delay.

16. check done

17. power off and connect motor, check correct operation by pressing limit switches.

edited: add item 12a.
 

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Thread Starter

strpdbas

Joined Dec 24, 2008
99
Hello, and thanks for the troubleshooting chart. I started testing boards today and was able to isolate a bad 555 using your list. I do have one area which caused a problem on one board so far. At min delay of the VR all is fine but if I increase the value anywhere above minimum the lights don't come back on. I removed the VR and it tested fine. What else could cause this problem?
 

eblc1388

Joined Nov 28, 2008
1,542
At min delay of the VR all is fine but if I increase the value anywhere above minimum the lights don't come back on. I removed the VR and it tested fine. What else could cause this problem?
The timing capacitor C8 100uF is probably leaking badly or being inserted in the PCB with reversed polarity. Replace it.

You can place a DVM on 555's pin#6 and observe that the pin voltage does not rise from zero to 4V during the timing period as it should if all components are good.
 

eblc1388

Joined Nov 28, 2008
1,542
Is it OK to connect the lights to test the boards with the motor capacitor installed?
I would think so. I have completely forgotten about that capacitor on the PCB.

So instead of completely turns off, you will see one lamp brighter than the other.

If that isn't the case, then you might have to leave the soldering of this capacitor last after you have confirmed the correct operation of the whole PCB with lamps.
 

Thread Starter

strpdbas

Joined Dec 24, 2008
99
Fortunately the US & UK have been allies for a very long time!! I can't begin to thank eblc1388 enough for all of his help and patience.
 
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