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.NET Gadgeteer Module (FEZ Spider)


Hey Guys,

I am designing a module for my senior project (Electrical Engineering). This module I need for my project is going to have a power supply that will convert 120Vac to approx 7-10v (its going to be variable). This will help drive a solid state relay system instead of the mechanical relay module. My question is what is the max current I can pull from the +3.3V or 5V sockets? This will be used to turn on the SSD relays. I read the module design guide and socket guide but I cannot find this answer. The board I have is the FEZ Spider.

Thanks in advance,


40mA is usually considered the absolute max for FEZ boards. Don’t try and drive anything directly off the pins.


Are you talking the maximum current you can pull from a digital signal or from the 3.3V or 5.5V power pins on the sockets?

The 40ma number given by Ian is correct for digital signals, but as the current draw increases, the voltage drops. At 40ma the voltage may too low to trigger a solid state relay.


It seems to me you’re wanting to know the current you can consume from the power supply circuit, not what you can use from a pin to turn on / off the control circuit. That largely depends on the overall power supply itself, although I have to say given the power-in on any Gadgeteer board is powered down one wire in one of those pretty small connector wires, you may not have amps at your command…


Thanks for the answers guys. :slight_smile:

@ Mike: Wanting to know what was the max current that I could pull from the 3.3V or 5V power pins in each socket but it would be nice to know that max current of the digital signal pins which is 40mA.

Well I was wanting to know if I could pull power directly from the 3.3V or 5V pins off of a socket to turn on a solid state relay (using a digital pin as the on/off) but I needed to know if the FEZ was capable of that. Sounds like I need to pull that turn on current from the powersupply I need to design and use a transistor or mosfet as a buffer. I was trying to see how the mechanical relay module did it but I could not open the schematic files.

Hope that makes better sense.


@ Weston - You should be able to power a few relays (depending on the relay) from the power supply in the socket w/o problem. Are you familiar with this module?


Yeah, I saw it. i downloaded the support files for it but was unable to open the files (to view the layout and schematic of it)


Your best bet is to sink/source virtually no current through the digital pins. That gives you the greatest margin of error, and allows compatibility with the largest possible number of mainboards.

Transistors, LED drivers, etc are your friends :wink:


get the Relay Schematics from NetMF source code at Codeplex… open Hardware version 1.0 and not version 1.1 as that one is corrupted…



Thanks, I will give that a try :slight_smile: