View Full Version : First-timer design question

06-18-2005, 05:08 AM
This is a repost from the Javelin forum, but it isn't really specific to the Javelin.· I was really surprised not to get any responses yet.· A Yes or a No would be great.· :)

Hi.· I'm new to the forum, and new to the world of the Stamp.· I'm also a very novice electrical guy.· I am attempting to design my first stamp controller application, and would like some input.· I'm looking at using the Javelin.··I will have the following inputs to·monitor: 10 temperature sensors and·6 zone valve end switches.· I will have outputs of three pumps and six zone valves.·

For the inputs, I was looking at using 2 ADC0838 ADC's.· For the temp sensors, I was going to use AD592's with resistors to feed the ADC.· The zone valve end switches basically provide a 24VDC feedback that the zone valve is completely open.· I was going to use a 1/6 voltage divider to bring that down to a 0V/4V signal to feed the ADC.

For the outputs, I was looking at using 2 8574's on one bus.· One would run the 6 zone valves.· Is it correct that I can take the output from·a pin·on the 8574, feed it to a (transistor | mosfet), which would feed a relay, which would energize the pumps?· One pump is 120VAC, the others may be as well, or may be 12 or 24VDC.· The datasheet on the 8574 says the pins stay latched, so I'm assuming I can do that, and just send a 0 down the line when I want them to shut off.· The zone valves are basically just 24VDC solenoids, and would operate the same way.

I would also be using a 1302 real-time clock chip, and an LCD display.· It looks like this will take 14 of my 16 I/O pins, and do exactly what I want it to.· Are my assumptions correct, or am I way off base?· Thanks.

06-18-2005, 11:10 PM

I quick review of your idea seems like it will work. I could not find a data sheet on the 8574, but I assume it needs three stamp pins to operate, and it can be daisy chained.

You might want to consider some type of opto isolator if you are going to switch 120vac. I have never done it with a micro, however it seems many in these forums have reported problems like programs resetting or other strange phenomenom when switching 120vac without using opto isolators.

If you look in the EFX forum, I think Jon Williams has selected a crydom that is interfaced to the stamp and it switches 120vac without strange phenomenom.