Solenoid switching without relays

Question

I have a latching solenoid that operates on 2vdc (at the lowest) all the way up to (as I have tested) 9vdc - the minimum amount of current I have tested it with is 0.01A (which is the lowest my benchtop power supply with provide).

EDIT: The side of the solenoid reads DC3v 25ms 0.02-0.8MPa.

To operate the solenoid it has two leads, apply voltage across the leads in one direction to actuate it in one direction and then apply voltage across the leads in the opposite direction to actuate it the other way.

I want to control this solenoid via a nodemcu ESP8266 and I have confirmed that the 3.3v pin to ground will actuate the solenoid, but I cannot for the life of me figure out how to get this operating without using relays.

I feel like at 0.01A 2vdc minimums that I should be able to set a pair of digital pins as outputs and trigger one of them high and the other low to make the circuit flow, but this does not appear to make the solenoid trigger. I have tried all kinds of different configurations of transistors to make this work and I still come up empty handed. Short of making my own H-bridge (which I tried, but I am unable to sort out correct combinations of resistors/diodes/transistors to make it work since I am still learning) do you guys have any suggestions for how I could accomplish this in the simplest way?

NOTE: I know I can do this off of a pair of relays easily, which I have done and tested - but this is an exercise to see how to get this working without them using, for instance, transistor logic for fun.

I know I can buy an off the shelf H-bridge motor controller board and make this work, but that isn't really the exercise I have given myself here.

I have been banging my head against a wall for the last few days trying to sort out how to do this and have come up empty handed, so that's why I am here haha

Answer 1

Here is a simple building block that could provide part of what you need. I'll leave it to you to figure out how to complete the circuit to drive your solenoid. (This is my first time using the schematic editor - I usually use LTSpice).

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

You can use a push-pull emitter follower H bridge. Almost any NPN and PNP transistor will do, they don't even have to be complementary types. K1 is the relay coil. C1 conducts when either side of the bridge is turned off - it is a snubber, together with K1's internal resistance. A resistor may need to be added in series with C1, since K1's resistance may be on the low side in a 3.3V coil.

^{simulate this circuit – Schematic created using CircuitLab}

When GPIO1 and GPIO2 are at the same level, K1 sees same potential across and the currents across it will decay away. When GPIO1 and GPIO2 are at different levels, current is driven across K1 from supply to ground, in a direction determined by which GPIO is high.

There are always two diode drops (2xVbe) in series with K1 in the circuit above. If you'd want to avoid that, then two push-pull common emitter stages in an H-bridge arrangement will work:

^{simulate this circuit}

Q5-Q8 switch the GPIO voltages to bases of Q1-Q4. The latter are common-emitter amplifiers. The voltage across K1 is the rail voltage minus 2 x saturation voltage of Q1-Q4/Q2-Q3.

The above circuit can also work from a single 3-state GPIO port: to turn K1 off, GPIO has be configured as an input:

^{simulate this circuit}

Answer 3

If you feel like living a little bit dangerously you can try a 74LVTH125

^{simulate this circuit – Schematic created using CircuitLab}

This should give you typically around 3V across the coil @10mA so it should drive the coil properly.

If you want belt and suspenders, attach 4x 1N5819, one from each side of the relay coil to GND and one to 3.3V, reverse biased of course.