# How to build this circuit.

#### tomdtc

##### New Member
This needs to fit in a housing about the size of a ink pen. 1 led light with a on/off switch thats a solid light when turned on then starts blinking after about 60 seconds until turned off.

#### gophert

##### Well-Known Member
Most Helpful Member
It sounds like overkill but s single microcontroller can do this most easily in the smallest space. The size can get extremely small so you'll have to let us know if this is a diy project or something that automatic pick and place equipment will assemble.

How many of these do you need? One or thousands?

How will it be powered?

How bright of an LED do you need?

How fast does it flash (on time, off time)?

#### tomdtc

##### New Member
Hi, Thanks for responding. Its a diy project. The cost will determine the quantity. I was thinking a small watch type battery that would fit in the pen size cylinder. 1.5vdc I guess. A regular led should be good. The flash rate won't really matter. Is the microcontroller and power all this needs? What would the part cost about?

#### gophert

##### Well-Known Member
Most Helpful Member
Hi, Thanks for responding. Its a diy project. The cost will determine the quantity. I was thinking a small watch type battery that would fit in the pen size cylinder. 1.5vdc I guess. A regular led should be good. The flash rate won't really matter. Is the microcontroller and power all this needs? What would the part cost about?
Once designed, plan for 1000 pieces...
$0.50 for the microcontroller,$0.25 for the pcb
$0.25 for the LED$0.50 for a decent battery
$0.35 for a microswitch$0.30 for assembly
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#### tomdtc

##### New Member
What I'm looking for is a simple circuit to light a led after a 60 second delay. Ideally it would start via a thermal sensor at about 90 degrees. This is for a cooking device, and no it's not for drugs. It could shut off when removed from the heat source or a switch.

#### ChrisP58

##### Well-Known Member
What I'm looking for is a simple circuit to light a led after a 60 second delay. Ideally it would start via a thermal sensor at about 90 degrees. This is for a cooking device, and no it's not for drugs. It could shut off when removed from the heat source or a switch.
90 degrees what? Please note that this is an international forum so, since temperature is measured with different scales in different parts of the world, you need to specify which scale you're using.

The PIC10F320 has an internal temperature indicator. That should work unless you need to measure the temperature remotely from the chip. Then a thermistor may be adequate. What level of accuracy do you need?

How high of a temperature does this thing need to withstand? Not just in normal use, but if the chef gets distracted and something overheats?

https://www.microchip.com/wwwproducts/en/PIC10F320

#### tomdtc

##### New Member
It does not have to be that accurate. Its purpose is to start the timer. The temperature will reach around 115 celsius at the devise.

#### ChrisP58

##### Well-Known Member
There is a version of the PIC10F320 that goes up to 125°C. And you should be able to find high temp versions for most of the rest of the components.

The problem will be the battery. Typical max temperature for a Li-Ion cell is 60°C. There may be some high temp versions that may go a little higher than that, but going up to 115°C is very unlikely.

Other chemistries have different max temperatures, so you might find something to go up that high.

#### Nigel Goodwin

##### Super Moderator
Most Helpful Member
Funny how it's suddenly changed entirely, and got a LOT more difficult.

Use a separate probe, and keep the electronics out of it - there was never any mention of it needing to be water and heat proof.

#### tomdtc

##### New Member
I was not very clear about the application. There will be a metal rod that is subject to the higher temps. The components would be in a handle attached to that. And its not that funny, I just have an idea and exploring different options on how to make it so.

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