I keep frying my sensors - Page 1
Forum section: electronics / beginners

author: human
author_rank: Newbie
timestamp: April 22, 2022, 10:28:13 am
content: So I started my first electronics project a few days ago. I want to climate control a fridge using an arduino, but i want to power everything from a separate source, i.e. a 24V power supply and then use step down converter modules to get the correct voltages for the different components.I started off and everything worked fine for a while. I started off with a breadboard with cables running everywhere and it was a mess. I accidentally yanked everything and after that i got weird values from my arduinoSo either I fried my sensors or I fried the board. But I bought new sensors, redesigned the "breadboard" to become a more "screw up friendly" (see image), and tried the sensors separately, and they worked like before. But when I hooked everything up again and the sensors got fried instantly.I measured all the voltages using a voltmeter and they are spot on. But I'm guessing there might be some transients when i connect/disconnect the power supply(?).So any ideas what the problem can be? I don't have any fancy resistors or any back EMF protection because i don't know that much about electronics and thought it would be plug and play ^^, I only connected all sensors to the positive and negative/zero, and the data-signal to the arduino and the GND of the arduino to the negative.More details regarding the setup:(I attached an image of how i did it with the power supply and the step down converters)1) 24V directly from the power supply to power a ultrasonic fogger (was not connected at the time)2) 12V to power a fan3) 5V to power 1 temperature sensor (DS18B20), 1 humidity and temperature sensor (DHT11), and a relay module x4 for arduino.4) USB from my computer to power the arduino, but the ground is connected to the negative.What do i need need to do to protect my sensors?

author: Psi
author_rank: Super Contributor
timestamp: April 22, 2022, 12:51:45 pm
content: My guess would be a grounding issue and perhaps not being aware of what you can and cannot common together without causing a short somewhere else.Are you aware those china DCDC modules have a common ground between the input and the output. They're not isolated.Another possibility is that black brick PSU you are using. It's probably isolated but the output may have ~100V referenced to mains earth at low current. (Due to the Y2 class capacitor from the mains side to the output rails)So when you plug the USB cable into your PC (which is earthed) you are shorting this ~100V to ground and when you have the USB cable disconnected you have ~100V of potential around your circuit just waiting to fry something.

author: human
author_rank: Newbie
timestamp: April 22, 2022, 02:16:41 pm
content: Thank you for your reply!I check it out and either of the GND-ports(it has two) of the arduino works to make a common ground, and i did hook the arduino's GND up to the negative side. So the PSU and the arduino should have the same ground.Regarding the DCDC modules, if they have common ground between the input and output, that should be a good thing right or will that be an issue?The last part sounds bad! How would i go about and protect my circuit from that type of spike? Should i add an inductance to smooth things out, or do you have any ideas how should i properly ground and avoid this?

author: Psi
author_rank: Super Contributor
timestamp: April 23, 2022, 04:37:31 am
content: Quote from: human on April 22, 2022, 02:16:41 pmDepends how you are using them. Are you doing anything with negative voltages? If the answer is no then you are probably fine.Quote from: human on April 22, 2022, 02:16:41 pmIt's just a downside of using that sort of power supply. Some are worse than others.Sometimes you will see a tiny spark when the metal case of the USB plug touches the metal of the desktop PC's USB socket, which is bad.Or get a mild shock if touching both together just before you connect them, which is also a warning sign.

author: tepalia02
author_rank: Regular Contributor
timestamp: April 30, 2022, 06:00:36 pm
content: If the sensors are working separately, the problem may occur due to a bad breadboard. Sometimes, low-quality boards create problems. Also, sometimes there are bad jumper wires. So, kindly check the continuities of your jumper wires too. Also, check if any short circuit is occurring somewhere. If you face any issues regarding the DHT11 part, you can see this tutorial too:https://www.theengineeringprojects.com/2017/08/dht11-arduino-interfacing.html