Recommendations for new project

[mlaymance]

I am currently working on a project where I would like to use a picaxe. Let me see if I can provide enough information to start.

I have a sequencer that operates on AC voltage. It uses a coil heater to heat an element that closes contacts. The resistance of the coil determines the time it takes it to heat enough to close the contacts. When the voltage is removed, the coil cools and causes the contacts to open. This unit has anywhere from 1 to 6 sets of contacts. (different models). Each set of contacts are timed differently.

My goal is to test these units to to check for proper timing and duration. Here is the data that I use to determine that, and would like to capture this data and send it to a computer screen:

1. The amount of time from the start of the test until each set of contacts closes (TTC-1, TTC-2, TTC-3, etc.).

2. Duration of the closure.(CD-1, CD-2, CD-3, etc.).

3. Total test time. (From start of test until all closures re-open).

As soon as all of the contacts close, power will be removed allowing the contacts to open up (as the coils cool down the contacts open).

Side notes:
These devices are used in the HVAC industry.
1 output for driving a relay to turn on the AC voltage will be necessary.
1 output is necessary for an Test in progress Indicator.
1 Output will be necessary for a completed test indicator. (Indicators will be LED's). The timing is not "critical" and only needs the accuracy of 1-2 seconds.

I am thinking that A 28X will work, but not sure if something smaller will. Data will be printed using a screen print function.

I assume that storing the times in registers then reading the registers would be the proper way. Inputs to the picaxe could be provided via Opto-Isolators?

Thanks in advance for any information/insight you may have.
Any Ideas would be appreciated.

 

[womai]

Sounds perfectly feasible with a Picaxe. As for pins, don't forget two pins to send & receive data between PC and Picaxe, and probably 1 pin per contact (to read the state of each contact).

I'd use a 28X2 because apart from a sufficient number of pins it also offers a hardware time & timer interrupt - very handy to keep time in the background. That way the timer counts the seconds (or 1/10th of seconds), and all your main routine has to do is detect when a certain contact closes (or when the test is finished) and record the current timer value at that point.

Since your project doesn't sound like it has to be highly portable or extremely small I would NOT shoot for the smallest Picaxe possible that seems to fit the bill. From experience I can tell that you will always find out that you forgot something that required more memory or I/O pins, and if not, you'll come up with some ideas for new features and imporvements that result in the same. So it's good to leave some headroom.

Wolfgang

 

[DTB Radio]

This may not be much help, but why not combine the test-in-progress and test-complete indicators on the same output? A pair of parallel LED's wired in opposite directions on the same output pin would give exactly what you need, unless you want a third condition of no indicator at all.

 

[mlaymance]

This may not be much help, but why not combine the test-in-progress and test-complete indicators on the same output? A pair of parallel LED's wired in opposite directions on the same output pin would give exactly what you need, unless you want a third condition of no indicator at all.

DTB thats a good Idea. The indicator is for someone else that may be using this device. Not necessarily for me but for them.