Simple on/off power device

I am in need of a simple computer controlled (through USB) device that will either open a relay for a specific amount of time (3-4 seconds) or power something on and off (i.e., a timed relay board requiring 5 or 12 volts) for a specified period of time (5-10 seconds during which the relay opens and then closes for 3-4 seconds). The device will be used to power up a piece of equipment that simply requires the opening and closing of a relay for 3-4 seconds in order to boot up the equipment. No power is to be fed by the device through the system to the equipment being booted, simply an open/close signal. The specific requirements are:

  1. The device should be both operated and powered through the USB port.
  2. No power is supplied through the system, simply an open/closed relay.
  3. In the second option the device being powered is a small timed relay board which needs power long enough to go through it’s 3-4 second open/close operation.
  4. In the second option the power supplied by USB port itself.

Our current system works just fine when using a Ethernet controlled AC power strip simply by turning an outlet on and off which then supplies the current timed relay board 12 volts for the necessary amount of time. Our problem is that we want to be able to send the relay signal without the use of the remote AC power strip with power instead being supplied by the USB port itself if at all possible. If necessary, we can power everything with a DC power supply though.

The first option would be ideal since it would eliminate the need for the second timed relay board. But either method will suffice.

Were it possible, this could all be accomplished through the timed powering on and off of a USB port but because that is generally not a possibility (either on a PC or a USB hub), this work around is needed.

One problem I have is that I don’t have any experience programming such a device so the programming cannot be too complicated but for this purpose I don’t think it should be. For the second option, one way that this could probably be accomplished is through a computer-controlled device that powers a DC motor on and off for the specified time which in turn would supply the 5-12 volts need to active the timed relay rather than powering a motor on/off.

Any suggestions on how to accomplish this would be appreciated.


We do not have anything that does this specifically, but there are several ways you might be able to build something like that with our products.

The coil on the relay on our SPDT Relay Carrier with 5VDC Relay draws about 80mA, so it should be possible to supply power to the board over USB. Our relay carrier boards have a FET onboard that drives the coil, so it is possible to use them with low current logic input with something like a microcontroller.

To provide a logic signal to the relay board from a PC over a USB data connection, one option is our Micro Maestro 6-Channel USB Servo Controller. Any of the 6 channels on the Micro Maestro can be configured as a digital output (like the Relay board I mentioned uses) and it is possible to toggle these channels using ether a native USB interface, or virtual COM port. You can find a user’s guide for the Maestro on the Resources tab for it’s product page

A cheaper option is to use a general purpose microcontroller board like our Arduino compatible A-Star 32U4 Micro (which has a USB interface) to toggle the input on the relay board. Unlike the Maestro, the A-Star does not come with firmware to interpret serial or other types of USB commands from a PC, so you would need to write your own to do this. The Arduino IDE does have example code for doing things like interpreting serial data and toggling I/O pins included and there are a lot resources for Arduino compatible boards like this online.