# PID control of NiCr wire

I need to design a controlling mechanism for heating a nichrome wire of 15 cm (to be specific 36 gauge NiCr wire ).

These are the following constraints

1)The Power source is 5volts from USB in PC.

2)The temperature range of nichrome wire should be between 30 to 60 deg Celcius.

Once the wire heats up to this temperature the power supply should be reduced and if temperature reduces it should heat up and maintain the prescribed temperature.

So i decided to use a basic rapid prototyping board - Arduino to control the supply to the wire via PWM output.

Since the current output from the GPIO pins of Arduino is in few mA ,i should use a driver circuit for heating the wire .

So here are my doubts

1) How to calculate the amount of current required to heat up the NiCr wire to 30 deg C with 5V usb supply.

2) Am thinking to use a mosfet to supply to the wire ,such that i will connect the pwm output directly form aurdino to gate of the mosfet .Is that feasible for these specifications ? Or i should use any other driver IC's

3)To control the pwm output ,i need to measure the current temperature of the NiCr wire and feed it into the ADC of arduino ,and based on the feedback i have to control the pwm output to the driver.

4) To measure the current temperature of NiCr wire ,i cannot use any temperature sensors or thermostats .I have to measure the resistance across the wire and relate it to the temperature.Here am struck with !

How to relate or create a lookup table to determine the temperature of NiCr wire based on the resistance of the wire.

• What resistance should the wire be in an ambient of X? How does this vary with changes to X? May 27, 2015 at 12:00
• One of the characteristics of NiCr wire is that the resistance is relatively constant as the temperature changes. That is one of the many reasons that it is used as a heating element in so many devices. You will probably need to actually measure the temperature in some fashion to provide the feedback that your PID controller requires. May 27, 2015 at 12:39