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Small circuit GPIO Beaglebone to other DEV PCB

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New Member

I'm a technician that is attempting to design a quick circuit for a project at work. My hands-on knowledge is extensive, but my design not so much.

Here are the basic situations:
DEV Modem PCB has two buttons:
Power On/Off - Active Low - Sits at 2.6V and when button is pressed it is tied to GND, which turns the modem off or on.
Reset - Active Low - Sits at 2.6V and when button is pressed it is tied to GND, which resets the modem.

We need to be able to simulate this button press instead with software from a Beaglebone Black, which runs at 3.3V. My idea is:
GPIO from Beaglebone into an N-Channel MOSFET Gate.
Power On/Off line from switch into Drain.
GND into Source.

Then when software turns that GPIO pin high, it will simulate a button press until it is turned low. Anything I am missing here? If not can someone help me spec out a MOSFET from digikey/mouser/Newark? The beaglebone again is 3.3V, and the Modem line 2.6V.

Situation two:
There is an SPDT switch that enables and disables RF from transmitting. We want to be able to simulate toggling this switch back and forth from a beaglebone GPIO pin. Each side of the switch has more circuitry than just a pin/gnd, so I don't want to try to control both sides somehow with GPIO pins. So I'm thinking replace the toggle switch with a solid state relay. The one I found that's a good fit uses 1.2V. Does this sound like a good idea:
GPIO 3.3V > Regulator converts 3.3V to 1.2V > Solid State Relay
When GPIO is high, the relay switches one way, when low, it switches the other way.

Thoughts? Thanks in advance!


New Member
Here's a switch

In the second case, I think the 1.2V might be the forward voltage of the LED in the optical relay.
If that's the case, you just need to limit the the current to whatever the datasheet decrees: a series resistor


New Member
Awesome thank you.

The 10K is a pull down correct? It keeps the Control In, my GPIO pin, at LOW instead of possibly floating, until I tell the software to set it HIGH?

I'll check my datasheet for the solid state relay. If you it would be a series resistor in-line with the Control Input of the solid state relay correct? The one I'm using has 6 pins. Control +, Control -, then two pins for a NC set of contact and two pins for a NO set of contact. I think I know how to figure out what resistor I need but it would similar to LEDs so in the range of 100-1000 ohms or so?


New Member
Here's a datasheet table: (LCA110)

Limit the drive current enough that the relay operates at all conditions you expect.
Frinstance, a 3.3V supply would give 20mA through a 1.2V diode with a

(3.3 - 1.2) / .02 = 105 ohm resistor
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