Triggering a Light Tree or Solenoid from a USB Port

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gpraceman
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Triggering a Light Tree or Solenoid from a USB Port

Post by gpraceman »

I've had a couple of GPRM software users run into problems trying to trigger a light tree or solenoid gate when using a USB to Serial Adapter. Unfortunately, some manufacturers are not making their adapters to the full RS-232 spec. The voltage supplied to Pin 4 and 7, which you can use to trigger these devices, may not be the full +/- 12V. The voltage could be much lower. Some manufacturers may not even implement the use of Pin 4 and 7.

So, if you run into a problem trying to trigger your light tree or solenoid gate via a USB to Serial Adapter, you should get a multimeter and check the actual voltage being supplied on the applicable pin to ground (Pin 5). If the voltage is too low to trigger your circuit, you could change your circuit to trigger off of the lower voltage or buy another USB to Serial Adapter.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
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SirStorm
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Re: Triggering a Light Tree or Solenoid from a USB Port

Post by SirStorm »

I would also suggest a possible solution-work around. Build a relay with supplement 12v power for the solenoid. The draw on the USB power could overload the motherboard. It would be safer to isolate the computer USB in any case. If your PC has a serial port, the specs for that were designed to drive actuators with high loads and are safe.
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gpraceman
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Re: Triggering a Light Tree or Solenoid from a USB Port

Post by gpraceman »

Most trigger circuits that I have seen use a MOSFET. You can switch out the MOSFET with one that requires less gate voltage.
Randy Lisano
Romans 5:8

Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.
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