Forum 2005-2010 (read only)
Arduino + multiple multiplexers (74HC238) problem
Topic: Arduino + multiple multiplexers (74HC238) problem
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Re: Arduino + multiple multiplexers (74HC238) problem
Jun 07, 2009, 02:15 am
Thanks a lot Mike!
In particular for that trick of using the software to enhance the pulldown, in the end i solved the problem hardware side, but it is likely to come in handy later in the project.
I agree with you completely on the unconventionality of the design and its problems. I had come to the same conclusion as you did regarding all the unpowered photodiodes pulling the line down, but actually after a lot of testing i found the major flaw of the design :
- i actually put only ONE pull down resistor at the end of the data line.
- i tested putting a pull down at each sensor and it solved most of the problem!
-then i replaced the pull down resistors with "pull down capacitors" (bypass capacitors if i remember right) with a value of around 100 mFarards and it solved both the noise on the line, and the pulldown problem
Now the thing is , i still think i need to change the design, while i am still in the prototyping stage : i really was trying to cut corners too much with the current design : so what i was thinking :
-switch back to analog multiplexers to get the values (which would be a "cleaner" solution: no problem there : i tested it on a breadboard works well
-problem is : i need to be able to power only a few of the photodiodes simultaniously since powering 350 of them constantly is impossible:
so any input on how i could do this is more than welcome (i though of either reusing a modified version of my current system with a few of the sensors in parallel instead of individually powered, or perhaps a led driver? )
Any input is welcome, as always!