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How do I flip a switch?

Started by GOT, September 05, 2008, 10:34:46 AM

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GOT

I want to use one of the older Cowlacious scary-terry control boards to play a sound.  I can trigger the sound by making contact between two pins.  My question is... how?  I think this is where I would use a relay, but I have not worked with relays and would have no idea which to use and the proper way to set it up.  Of course, I could just jumper the pins and supply power to the board when I want the sound but I think this approach would cause unnecessary stress on the board.  Any suggestions?

http://www.cowlacious.com/SupportDocs/Scary%20Terry%20ASD%20Manual%20for%202005%20-%20regular-v2.pdf

GOT

By the way, this is what the manual says about the trigger pins: 

TRIGGER WIRES (Works only with units using the ISD ChipCorder
option.)
A set of trigger wires is provided for your convenience. The trigger
wires allow you to easily trigger the device using an effect timer, step
pad, motion detector, switch, etc. Just remove the RED jumper that is
attached to the trigger pins and replace it with the trigger wires plug.
Then connect the trigger wires to your triggering device. The triggering
device should provide a set of dry contacts that do not send any
voltage to Scary Terry's triggering pins.

JonnyMac

No problem you can do that -- I have.  What you need to do is suss out which of the two pins on the Cowlacious board connects to ground.  The other pin will be an active-low input.  What you'll do is connect the Prop-2 GND terminal to the Cowlacious ground pin, and then connect the OUTx terminal you'll use for control to the other.  If you pulse the OUTx pin for about 25 milliseconds (that's what I've always used) the Cowlacious board will start.  If you leave your control pin high the Cowlacious board will loop.

Assuming that pin has already been defined as an output and low, you can "blip" the pin like this:

Start_Audio:
  PULSOUT CowPin, 12500


This works because PULSOUT toggles the pin state for the desired time (expressed in 2 us units).  When the time expires the pin returns to its original state -- this is why you have to predefine the pin as low.

Here's an older Cowlacious audio player connected to a Prop-1 as described above.  Note that I'm powering the Cowlacious board from the Prop-1 so the ground connection has been made.



Jon McPhalen
EFX-TEK Hollywood Office

GOT

Sorry, I'm new to all this.  How do I determine which pin is the gound pin?

JonnyMac

The safest way is to remove power from the Cowlacious board and use a continuity tester; you want to look for continuity between the pin and the negative power supply input.  Sometimes you can just follow the traces on the bottom side of the board; be careful, though, the visual method is not always reliable.
Jon McPhalen
EFX-TEK Hollywood Office

GOT

I don't have a continuity tester.  Could I use a diode or LED to see which way triggers it?  Would there be any damage to the board if I got it wrong?

JonnyMac

So long as you don't have the power supplies connected together a reversed connection on the trigger input *shouldn't* hurt anything -- but I would never take a chance and suggest that you don't, either. 

You can run down to you local auto parts store (or Harbor Freight) and get a cheap meter for a few bucks.  It would really be worth getting an inexpensive meter -- it will come in handy with this project and others.

Harbor Freight: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92020
Jon McPhalen
EFX-TEK Hollywood Office

GOT

OK, I have one of those already.  I guess I am clueless about how to use it to find the ground.

JonnyMac

You should have a continuity check function on it.  In this mode touching the leads together causes the meter to beep.  When you find this connect one meter lead to the negative power supply input (should be marked on the board).  Use the other lead to check the trigger input pins (one at a time); the one that causes the meter to beep is the ground side of the trigger input circuit.
Jon McPhalen
EFX-TEK Hollywood Office

ScaryTinker

GOT,

Some cheapy meters like the Harbor Frieght model don't have a continuity checker mode.   I'd suggest setting the meter to read ohms (the omega thingy), use the 20K range.   When there is not continuity the meter will read "1". If there is continuity the meter will read some value near "0".  At least that's how it works when I test the voltage regulator and ground connection on the Prop-1

menehune

Typically, most circuits boards have a ground trace running around the edge of the circuit board.  Many times mounting holes are grounded as well and they have a circle of silver around the screw hole that is connected to ground. 
Voltage regulators can also be connected via their mounting screws (if they are TO220 type) to ground.  Regulators without mounting screws can be soldered to ground as well, since the ground trace acts as a heat sink.
Ground traces also occupy large areas of board that signal lines can't due to noise issues, etc.