Looking to make a circuit with just a lily pad coin battery, temperature sensor, and LEDs. The idea is that the LEDs will only light up when someone holds the temperature sensor to activate it/complete the circuit with their body heat.
I’m not using arduino or coding. It seems like a really simple idea but I’m having trouble figuring out how to build the circuit, or if the battery, temp sensor and LEDs have to be in a certain order for it to work.
Can anyone tell me what the order of the battery, sensor, and LEDs have to be—or how to connect it so the sensor works?
It could be done, but the tricky part will be finding an analog tempt sensor that is tuned to the relevant temps (not activated at ambient, activated around body temp…so not activated until like 90F)
Unfortunately it’s not as easy as connecting a battery, sensor and LED in a specific order.
The easiest way to do what you want to do is to use an[ Arduino and a little bit of code but you could use a comparator circuit made with an op-amp and some resistors and do everything in the analog domain.
Sadly, Sparkfun no longer carries a [comparator breakout board so you’d need to build your own. (or get [something else) The circuit in the link below might work for you but you’d need to source the components and modify the circuit to work on less than 12 volts.
What the circuit does is compare the voltage coming from a temperature sensor like a [TMP36 or a [thermistor to a preset level that’s set by a potentiometer. If the temperature sensor is outputting a voltage lower than the preset, the comparator doesn’t output a signal. Once the temperature sensor outputs a voltage higher than the preset, the comparator turns on an output and that could be used to light a LED. When the temperature sensor cools down, it’s output voltage falls below the preset voltage and the comparator turns it’s output off.
OP didn’t mention sensor response time, bulkiness concerns, orientation assumptions, or hazmat-free construction requirements so this must be the perfect solution! Low ‘idle’ power overhead, too.
