Could you please help me with the following issue. It is a basic problem but I need help anyway. Please refer to the picture below. Circuit.

In fact, I would like to use a proximity sensor in order to action a solenoid (a push pull button) when an obstacle is close to the sensor there is a 5V voltage between A0 and GND which I would like to input it to the selenoid to action it. However, when I try this circuit, the solenoid is not actioned. When replacing the solenoid with a LED, the voltage is not equal to 5V (it is equal to 2.4V).

Could anyone help to overcome this simplistic issue please?

  • 1
    \$\begingroup\$ Please edit your question to supply the datasheet (not an Amazon or Ali-what's-it ad page) for the sensor and the solenoid. Does the solenoid work when you apply 5 V directly? What is its resistance? How much current does it draw? How much current can your IR sensor supply? When you used the LED did you remember to include a current limiting resistor? What colour was the LED? Please try and answer each question. \$\endgroup\$
    – Transistor
    Commented May 26, 2020 at 22:50
  • \$\begingroup\$ @Transistor Thank you so much for you answer. Here is the sensor datasheet docs.rs-online.com/435d/0900766b80e309db.pdf and the solenoid one digikey.fr/product-detail/fr/sparkfun-electronics/ROB-11015/… (this is not the datasheet since the original one is in chinese). The solenoid works perfectly when applying 5V directly. According to the datasheet the resistance is 4,5Ohms. I did not find how much current the IR sensor supply. If can afford you in further needed information. \$\endgroup\$
    – YasARE
    Commented May 27, 2020 at 7:41

1 Answer 1


It's clear that the sensor is incapable of sourcing 1.1A required for the solenoid to actuate.

However, it's capable of lighting the LED and the voltage that's being read is the forward voltage of the LED.

A transistor driving a relay and a 5V DC power supply capable of sourcing 1.1A would be additionally required to actuate the solenoid.

Here's the schematic.

enter image description here

  • \$\begingroup\$ Thank you so much. Could you please suggest me references or where I can add the transistor in the schema? (I am a true beginner and I come from a different field). I have also another question: when I measure the voltage between A0 ang GND (when the solenoid is not connected) I find 5V. According to my understanding, since the resistance is fixed and the voltage is fixed, the current should adapt (accoding to Ohm law) isn't that correct? Thank you once again. \$\endgroup\$
    – YasARE
    Commented May 27, 2020 at 9:01
  • \$\begingroup\$ You are most welcome! When you light the LED, 2.6V is dropped by the transistor with 2.4V measuring across the LED. Without the solenoid, you are measuring the 5V at the sensor output. The required current will flow only if the source is capable of delivering it. Please furnish the schematic of the sensor and details of the 5V supply so that the necessary changes may be incorporated. \$\endgroup\$
    – vu2nan
    Commented May 27, 2020 at 11:07
  • \$\begingroup\$ I do really appreciate your help. The datasheets are in the comments of the previous comment. For the 5V suppply, I al using currently arduino but I am planning to use commercial battery. \$\endgroup\$
    – YasARE
    Commented May 27, 2020 at 12:16
  • \$\begingroup\$ Hi YasARE, My schematic has been included. \$\endgroup\$
    – vu2nan
    Commented May 27, 2020 at 16:26
  • \$\begingroup\$ Thank you @vu2nan. I am trying to understand the schematic. Can you please give few explanations please? \$\endgroup\$
    – YasARE
    Commented May 28, 2020 at 8:04

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