I need help building a circuit with a built-in timer.?

Question

I am trying to build a circuit that has a built-in timer that can be started and count until a switch within the circuit has been shut off. If this information can be displayed on an LED, that would be simplest. Ideally, the time information can be stored within a chip and either manually retrieved or wireless transmitted. Any thoughts? I can clarify if needed. Thanks.

Answer 1

Here's some nice links on microprocessors. I would go with the $50 board from PIC per the link.

http://answers.yahoo.com/question/index;...

You could also use a bottom end PLC; the basic unit runs about $100 + real time clock + display + software if going with a serial port is OK, the ethernet card is additional. Datalogging interface software is kind of pricey

http://web5.automationdirect.com/adc/Sho...

Good luck!

Answer 2

Rather than build a logic and timer circuit, you could simply purchase a programmable micro-controller, like the PIC series.  You could hook a few 7-segment LED displays to it, and upload/download info to computer over a serial (wireless or usb) connection.

Answer 3

sure. Nothing complicated here. How accurate do you want it, and what resolution?

There are lots of timer chips, and xtal oscillators, there is one in every wrist watch and clock, after all.

You pick a counter IC, or several, depending on how many digits of readout you want, and what format (binary, decimal, hr-min-sec), and have them drive 7 segment decoders, and those drive 7 segment displays. The counters have set-clear pins so you can use those.

If 1 second resolution is enough, get a xtal oscillator and divide it down to 1 pps via a different bunch of counters. Use the 1 pps signal to clock the main counters, the ones connected to the displays.

All the above is fairly standard, that's what a clock does.

Since the counters have memory, they will store the data for you. you can read it out via the displays or gate it into a parallel to serial converter for transmission to a transmitter.

PS, unless you have lots of experience with counter circuits, go very slow, read the data sheets on the counter ICs carefully until you understand them completely, and build and test the circuit just a bit at a time.

edit: "Would the timer be able to store several trials and then have the data downloaded to a computer?"

even more complicated, but can be done. Put a set of memory ICs and logic to gate the counters into the memory, plus logic to read back the memory, and logic to set and change the address of the memory.

Unless you can find some LSI chips, I'd guess you are approaching 100 ICs.

In these kinds of circuits, you need a good PC board with a good ground and power distribuition, with bypass caps for every IC.

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