5V Relay Rapidly Clicks On and Off When Sensor Reads Above Threshold Value

Other Hardware Sensors
1

Hello,

I have a circuit made up on 8 C Cell batteries, an arduino nano, a 5V relay, amber LED, two fans (data sheet listed below), and an MQ2 Gas Sensor.The circuit is designed so that when the MQ2 sensor reads above a certain threshold value, which is set as 1.3V right now so that it triggers when smoke from a blown out match hits it, it triggers the rest of the circuit which is that for 5 seconds it runs the two fans, and blinks the LED. The MQ2 gas sensor is powered off of the 5V pin on the arduino.

The fans need 12V to run so it is set up so that once the arduino reads above the value at the analog pin, it sends a digital signal to the relay so that it can connect the fans to the 12V supplied by the batteries. Another digital pin then blinks the LED. This all works 100% when connected via USB to a computer for power.

The problem comes in when I try to run the circuit off of the batteries alone. I have a toggle switch set up between half of the batteries so that when it is switched on, 6V is used to power the arduino at Vin. This appears to work fine, as nothing is standing out as wrong at this point. Once I introduce the smoke, the sensor reads it and triggers the function for the 5 seconds, however, this is where the problem lies. The relay, instead of kicking on for 5 seconds and running the fans, rapidly switches back and forth never actually running the fans. The digital output seems to do the same, where instead of a slow blink with a delay of about 1 second, it rapidly blinks on and off.

Any help would be greatly appreciated, and thank you in advance
Mark

PS: Here is the data sheet for the fan if need be.

http://portal.sunon.com.tw/pls/portal/sunonap.sunon_html_d_pkg.open_file?input_file_name=7264646F632F3230313430312F3137363539372F28443132303137313330472D3030292D322E706466

2

Reads like a power issue.

Have you disconnected the relay's output and just run the relay coil, adding one device to the relay output till failure happens?

3

I have not, I will try that now!

4

It turns out that this is exactly the problem. Once I disconnected the fans, but left the sensor and LED attached, it ran as it should. Is there any way around this problem with the current set up of the circuit? Would more voltage to the arduino nano itself help in any way?

5

MarkBoudreau:
It turns out that this is exactly the problem. Once I disconnected the fans, but left the sensor and LED attached, it ran as it should. Is there any way around this problem with the current set up of the circuit? Would more voltage to the arduino nano itself help in any way?

You might sit down and figure out how much power you'll be needing to run your project. Take your fans, they might have a wattage rating on them, you can then figure out current draw. You can use a DMM and measure the actual current draw that the project is using minus the fans. Once in the ballpark with how much power your going to want, I would, now this is just me, get some 18650 batteries. With 18650's you can, also, add in a charging circuit.

Also, I am sure you'll get other suggestions for supplying power.

6

Okay, thank you very much for your help!