Concept circuit

I would like to drive a pneumatic relay from a TTL GPIO source, the TTL may be 0-3.3v or 0-5v I would like supply and cut 12v to the relay to control the air. I have a concept of what i'm trying to do in the circuit but my electronic design skills have not been used i a long time. I'm happy for other suggestions e.g. MOSFET etc. I would like use common parts available from Jaycar to solder on to veroboard

The datasheet for the relay says 16W (27VA) but I think its actually much less because I have driven 2 relays with a single 15W power supply with no problems.

Can someone provide me with a layout that can do such a thing and can work even if the load is much smaller e.g. 0.1W for example.

  • \$\begingroup\$ Rb>=1k or > 10x load R else burn out base-emitter. Read more about Relays. But Best Buy is an opto relay card then add reverse diode across load coil of solenoid \$\endgroup\$ – Tony Stewart EE75 Mar 6 at 4:42
  • \$\begingroup\$ The 2N3906 is only rated for 200 mA continuous. You'll need a larger transistor if that relay is really 16W @ 12V. It would be best to post the datasheet for the relay. Many pneumatic relays are intended for 24V and driving them at 12 means you are not reaching the rated current. This may be why you don't think they are 16W. \$\endgroup\$ – ScienceGeyser Mar 6 at 5:29
  • \$\begingroup\$ Relay datasheet please. Is it really a 12 V relay? Or something else? It's nice that you quote from it but I'd like to see it for myself. \$\endgroup\$ – jonk Mar 6 at 5:36
  • \$\begingroup\$ valvesonline.com.au/14.4mm-solenoid-coil valvesonline.com.au/square-din-plug-with-led#inline. I'm using the 10~50v AC/DC DIN plug and the and the SN14N coil \$\endgroup\$ – Beraben Systems Mar 6 at 6:54
  • \$\begingroup\$ BTW I just bought couple of BD681G BD862G transistors (and some 5v relays if all else fails ;) ) \$\endgroup\$ – Beraben Systems Mar 6 at 7:07

It seems you want to drive a solenoid valve using common parts and control it with TTL input such Arduino device?

The common approach for DIY level, is to use NPN transistor (BD681G On Semi could work) to drive relay that then switches on the solenoid valve. Note fly-back diodes are required across inductive loads when switching to avoid device failure (i.e. relay coil and solenoid coil). Example in link below: https://web.cecs.pdx.edu/~eas199/B/howto/fishtank/wiring/solenoid_wiring.html

The power rating for model SC-N14 DC12V version indicates holding power. When first powered on the in-rush current for relay can be about 2-3 times, select components accordingly. For DC solenoid valves there's no large in-rush current but for AC there is (edited). https://www.ia.omron.com/support/faq/answer/36/faq02165/index.html


An example circuit would be using mosfet with low Rds resistance. Flyback diode selected to withstand max current from solenoid. Pull-down resistor at gate of fet to have default state. The NPN BD681G cannot be used reliably in this configuration as the on resistance would cause voltage to be about 1.5volts less than 12V (large Ron resistance), voltage divider would also be needed to avoid exceeding Vbe_max.

Example schematic

  • \$\begingroup\$ Its not a Arduino device, and technically its a TTL output not input (but I understand what you meant so lets overlook that one). Also the circuit you provided has some subtle differences to what I am requiring i.e. your transistor is driving a 5v relay however the question was regarding the transistor configuration of driving a 12v solenoid with a 5v TTL signal. \$\endgroup\$ – Beraben Systems Mar 6 at 10:33

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