[roger.rrgt]

I am trying to make this reserve light with a 1k NTC in series with a 3 or 4 watt dash bulb and it works great at the bench with a 12V 1A source, but a car battery has way more juice than that, so the little thermistor fries very quick. What can i do to not fry our little friend? a less powerfull bulb maybe? Im not an electronics expert, far from that. The less parts the better.

[PSIG]

IMO (without datasheets) you are likely pumping too much current through the thermistor, and it's overheating. Check the datasheets for the maximum mW yours can take, and design the circuit around that. The bulb sets power requirement for lighting, the thermistor sets the allowable current, and the two work together as a balanced set. You need a smaller mW bulb or LED, or a more robust NTC, or an amplifier to use a weak NTC with a big bulb, etc.

OEM low-fuel thermistors are usually rather large and metal-cased to dissipate heat, and often have an inline control board. So, another option could be to cannibalize a complete working setup from a vehicle. Good luck, and let us know what you settle on.

[roger.rrgt]

Cant find the datasheet or the brand, only know it is a 1k ntc . I tried with led lights with all sorts of resistors and couldnt make it turn off, probably the difference in resistance between hot and cold is about 300 to 400 ohm, only enough to dimm it. I wanted to avoid an amplifier, but thats the best bet.

OEM low-fuel thermistors are usually rather large and metal-cased to dissipate heat, and often have an inline control board. So, another option could be to cannibalize a complete working setup from a vehicle. Good luck, and let us know what you settle on.

The casing was salvaged from a midnight 950, no idea how and where is this thing wired on the bike, maybe the dash circuit does the job, not an option.

[theonewithin]

Perhaps look at doing a voltage divider and connecting to a free analog input of Speeduino.

And program up an output to turn on when voltage gets to X and have a delay so it doesn't turn on and off to quickly.

That would get around missing any magic circuitry and put basically no load on the thermistor.

[roger.rrgt]

This is interesting, way easier than building the circuit on my own . What should i look for when doing it? With a calculator, the thermistor from the source, between 1k and 600 ohm and a 400 ohm resistor to ground give me 3,43-4,8V, less than 5v to not burn the mega pin. Something like this is ok?

[theonewithin]

Look at existing analog inputs and copy their protection.

And the wider the range, the better.