I need help with something I'm building because I've hit a dead end. I need this PIR sensor. PIR sensor

To activate this pump off a 9v battery.

solar pump

The problem is the power output from the sensor isn't enough to power the pump. I tried a transistor but still nothing and all my research has led me no where. I wired it up from a similar question asked on this site but it's still not working.this is what I tried

If anyone has any simple advice it would be greatly appreciated as I have zero knowledge of these things and only going on what I've researched off the internet. Thanks.

  • \$\begingroup\$ What happens when you use the circuit you included? What transistor was used for Q2? 800mW at 6V is about 130mA, not a lot of current- a single transistor may be enough, an appropriate 3V gate MOSFET certainly would be. \$\endgroup\$ Jun 28, 2014 at 18:08
  • \$\begingroup\$ Nothing happend with the pump, but when I switched in an led it stayed lit then would get brighter when the sensor activated. I used a 2N7000 N channel transistor. \$\endgroup\$ Jun 28, 2014 at 18:12
  • \$\begingroup\$ There is no pump element in the circuit provided? How are you driving the pump? Is the pump working? \$\endgroup\$
    – vyi
    Jun 28, 2014 at 18:22
  • \$\begingroup\$ Sorry, I should of said,The pump is where the LED box is, i assumed this circuit would work if I just switched the pump in. The pump does work when connected directly to a a 9v battery, I just need it to work off the PIR sensor. Sorry if I'm coming across naive, but I really have no knowledge of electrics, It's something I've just gotten into. \$\endgroup\$ Jun 28, 2014 at 18:26

1 Answer 1


A 2N7000 has too high a threshold voltage to reliably turn on completely with only 3.3V drive.

You can drive your pump with a single MOSFET such as this one.


simulate this circuit – Schematic created using CircuitLab

It's surface mount, but not scary lead pitch at all (TO-252). It will not require a heat sink if wired up correctly, and can switch on fully with 2.5V. Very few MOSFETs with low threshold voltage are available in through-hole packages (mostly older ones). They're around 50 cents in singles. R1 makes sure that Q1 switches off if the input is floating. D1 clamps any inductive transients from the pump motor.

  • \$\begingroup\$ Thanks for your help, it's appreciated. I will give this a go and see how I get on. Thank you. \$\endgroup\$ Jun 28, 2014 at 18:43

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