Solenoid without transistor

Borna

I have a small 5 volt solenoid ( https://www.sparkfun.com/products/11015?gclid=CJ-D7czR88ICFUpp7Aod5lEAug ) that I want to be able to turn it on and off using basic stamp II without the use of transistor.
Is it possible? I have been able to use transistor successfully, but due to some other issues I want to avoid use of transistor.

Thanks
Borna

Mike Green

You have to look at the datasheet. From what I can tell, you probably have the solenoid with the 7.5 Ohm coil. At 5V, this coil will draw about 660mA which is at least 20 times too much current for pretty much any microcontroller. You have to use a power transistor to use this solenoid. Note that you also need a "snubber" (reverse connected) diode across the solenoid coil to prevent the build up of reverse voltage as the magnetic field collapses when the current to the solenoid is turned off. This reverse voltage can destroy transistors and ICs (like the Stamp) if it's not dissipated by a diode connected backwards across the coil.

A Stamp I/O pin can handle about 20-25mA with additional limitations on the total current drawn by a group of 8 I/O pins (P0-P7 and P8-P15) and by the entire device (Vdd and Vss).

erco

Yes, per Mike a power transistor like a TIP31 could work, or a mosfet. You could also use a reed relay. Some of those only draw 20 mA at 5V and can be driven directly from a Stamp pin. Radio Shack sells one, but check the contact rating.

Mike Green

These small reed relays are very nice and do work with a Stamp I/O pin but you still need the snubber diode or the I/O pin may get zapped. They can't quite handle the current for the solenoid you've mentioned ... they're rated for 1/2A max. and the solenoid draws more than that.

I've used them for switching speakers. To minimize switching currents, I only changed the speaker settings when there was silence and the peak current, based on the maximum power output of the amplifier I used and the impedance of the speakers, was less than 1/2A.

You didn't say what the solenoid is supposed to do. Could you use a servo motor instead? Those can be directly controlled from an I/O pin since the servo has its own motor driver built-in.