View Full Version : Motor interference with 74HC595 chips

06-15-2005, 06:45 AM
I have a train/slot-car settup where I am using several 74HC595's to control things like train direction, crossing gates, traffic signals, etc. I also·am using several 74HC165's to detect the locations of the trains and slot cars. My problem is that my circuits work EXCEPT when my slot cars or trains are actually running, then the 595's go crazy, ie. the outputs start flipping randomly as if they were picking up interference from the train motors. I have no problems like this with the 165's.· I am using the PWMPAL and the Javelin controller but my question is specific to the 595's so I am posting to this forum.
Should I be using 74LS595's instead of the 74HC595's? Has anyone else had problems similar to this?

Thanks,· Mike

06-15-2005, 06:47 AM
Try putting a .1uf on the data line to the 595 as close to the pin as possible and see if that helps.

Sid Weaver
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Jon Williams
06-15-2005, 10:39 PM
Putting a cap on the data line would not be a good idea in my opinion; this may affect data to the 595. What you may actually need to do is pull the Latch line low with a 4.7K (or stiffer) resistor so that noise does not induce false latching. It would also be a good idea to bundle and shield the transmission lines to/from everything.

Jon Williams
Applications Engineer, Parallax

Alan Bradford
06-19-2005, 08:18 PM
Hi Mike,

Jon has a good idea·, in shielding the cables.

The best way to ground the shield is to use a ground near the noisey side of the cable and only ground one end of the shield. Now I assume that you do not have a good ground near your sensors, so ground them at the stamp end. Pick a spot near the ground side of the power supply and run all grounds there, including the one for the Stamp. This point should then be connected to a good Earth Ground. The Ground on the electric service should work here. MAke sure you use a 3 prong AC power cord (Assuming you are n the US..If not consult your local electric codes). If you are unsure about this then seek advice from a knowleagble electrican. Ths creates a central ground point for all noise. By only grounding one end of the shielded cables you avod ground loops. Each item to be grounded goes to this point and no where else. This is called a Star ground and is very effective in reducing system noise.

Is the Stamp sharing power with the Train/Cars? Ths may be where the noise is getting into the system.

Try adding a·.1 uf cap across the motors of each train/car motor.

Also add one to the output of the power supply(s) for the trains/cars.

If you are·powerng the Stamp·on the same AC supply, as the trains/cars,·try adding a niose filter to the Stamp Power Supply.

I use a CORCOM 1VB1 (Digikey Part # CCM-1300-ND) filter on the AC input to all my Industral Stamp Applications. This is a 1 Amp ac line flter. It costs around $13 US but is worth its weight in gold.

www.digikey.com (http://www.digikey.com/)

These practices should help you get to the bottom of your noise problems.

Good Luck,

Alan Bradford

Plasma Technologies

www.plasmatechnologies.com (http://www.plasmatechnologies.com)

PS: Can anyone tell me if there is a spelling checker on this Post Reply?

06-28-2005, 10:31 AM
I tried most of the suggestions and each one I tried made my problem get better, as in fixed my problem.· The caps across the trains/slot-cars where they get their power from the control board almost did the trick but then shielding the inputs to the 595's fixed it completely.· I went up to 1mfd from .2 mfd and it progressively got better.

Thanks a lot Alan and Jon!

It sure is fun working with this stuff and being able to ask for help on these forums when I have problems or questions makes it less frustrating too.