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Wiper motor controller circuit issue

1200 Views 1 Reply 1 Participant Last post by  Otaku
Hi all,
While helping DarkLore troubleshoot his motor controller board, I discovered a design flaw. It involves the use of Pin 1 of the 555 timer as the trigger that starts the oscillator. I have worked up a simple hack that solves the problem and will be posting pictures and instructions in the next few days.

The symptoms you may see with the original design are as follows: Continuous rotation of the motor, oscillator not starting, oscillator appears to be operating in "reverse" mode, and erratic behavior of the opto circuit. You also may not be able to interchange different versions of the 555 IC in the circuit i.e. one type (NE555P, for example) may work, while a MC1455 will not. Note that All Electronics is selling the MC1455 version.

These symptoms are due to the 555 being powered up with Pin 1 "floating" instead of being grounded. The fix uses Pin 4 (Reset) to control when the oscillator starts and stops, as was intended by the chip designers. I'm currently in the process of getting the test board optimized so that I can get clear pics of what needs to be done to eliminate this issue. I'll have pics and and a detailed instruction soon. It's an easy fix that requires the addition of two resistors, and cutting three traces on the back of the board. If you are comfortable with the assembly of the board, you won't have a problem implementing the fix. I've tested the fix with four different versions of the 555 IC and all are working.

Please note that this is not the fault of Jeff at Simple Circuit Boards - he burned the PCBs per my design and after I approved the schematics. He has suspended sales of the board until he gets back from vacation, and has the new layout in place. If you have any questions, please drop me a PM, or reply to this thread. I'll be happy to help!

Later: Here's a pic of the patch. You can see the trace cuts, jumpers and resistors. The resistor on the left is a 220 ohm, the other is a 1K.

HalloweenGallery.com - Documents/Controller patch
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· Bête noire
2,618 Posts
Discussion Starter · #2 ·
Hi all,
Just a note to those interested that Jeff's latest version of the board fixed the issue with the possible faults I listed above. I built out and tested the new version and it works perfectly. Thanks, Jeff, for the fast response!
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