pulsed input to timed output?

I'm planning to install the KH-300 media enclosure in my Jeep and control it through the IR-X repeater. However I would like a small screen to turn on when I first begin using the media remote, and stay on for ~3 seconds beyond the last button press.

PAC tech support suggested the TR-7 low voltage trigger, and even built and described a circuit similar to what I am looking for.

However, "it does not do exactly what you want becausethe output from the IR-X is not a very strong trigger signal & it pulsestoo rapidly, not all functions trigger it, and the delay 3 sec beforeturning off does not work because of this."

I had the best success withversion #11, programming it to see 1 pulse to trigger and 3 seconddelay. Like I mentioned earlier, not all the functions from the remotewould trigger the TR-7. From the looks of it, the TR-7 will not doexactly what you want, it was never meant to trigger off a data signal(IR signal).

I think the TR-7 still has considerable potential for my application. Does anyone have any suggestions about which function of the TR-7 might work well in a timed momentary circuit?

Perhaps two TR-7s, one to amplify and clean up the signal, the second to handle the output?

Thanks!

Spyderbyte

Should be pretty simple to just use a comparator to amplify the pulses to trigger your TR-7. You can go to mouser.com and search for "comparator" to find a bunch of suitable parts. Something like the LM311 should work- 34 cents and some assorted other items would do it.

You just have to set up a threshold on one input using a couple resistors (a zener diode if you need more precision), and then send your signal in to the other input. When the signal rises above the threshold, the comparator switches on, and you can use that to trigger whatever you want.

Would the following wiring diagram work?



Better yet, would that amplify the pulses enough for me to use a 528T Pulse Timer?

And final question, if the 528T recieves a second pulse while still outputting, does the timer reset and start over?

Thanks!

Spyderbyte

You probably need to set the threshold to something other than ground, because the way it works is that the output goes active when the signal from your IR-X goes higher than the other input.

If you just use ground as the threshold, it'd probably keep triggering from the slightest bit of noise, assuming the signal is normally sitting at ground when it's off.

Try setting the threshold to about 1/2 to 2/3 the signal amplitude, so it won't trigger from noise and makes sure it'll trigger when the signal comes in. If your IR-X signal is 250mV, you could set the threshold to around 150mV, using two resistors, 82k and 1k to divide down your 12V.
The 82k connects to the 12V, the 1k to ground, and the middle would sit at a voltage of 12V x 1k / (1k + 82k). Connect that to the threshold input, and then, when your input signal goes above that level, the output should go active.

Where is the threshold voltage grounded? The following makes sense, but it would also create a constant (albiet very small) draw.



I know it won't hurt anything, but it's an odd feeling to know I'm intentionally draining away electricity. However the only other schematic I can think of is this:



Am I close with either one?

Thanks!

Spyderbyte

The first one would be the one you could use-
If 150uA (or 0.15mA) is too much a draw, you can just use larger values of resistors in the same ratio, like 820k and 10k, dropping the current through the resistors to about 15uA. It's only providing a voltage reference, so you can go as high as you want, until the input impedance of the comparator and noise becomes more of a factor.

There are positive and negative inputs on the comparator, and it makes a difference when you connect it; I assume your drawing omitted it for simplicity-

dualsport wrote:

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There are positive and negative inputs on the comparator, and it makes a difference when you connect it; I assume your drawing omitted it for simplicity-

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Thanks, I'll be sure to pay attention to that.

Any idea on whether or not this would be enough to trigger the 528T?

Thanks!

Spyderbyte

It should give you a 12V swing on the signal; should be enough.
Just follow the datasheet examples for the comparator you use.