Topic: Electronic component purchase, testing and interfacing
Yesterday my whole day was spent on S P Road, Bangalore for component and accessories purchase. After spending 3 days for purchase I could get the bare minimum. I am using LM35 for temperature sensing, IRF830 MOSFET for current control of the heater. LF356 op-amp for scale changing of MOSFET gate input voltage. The DAC is giving the analog voltage of 0 to 3.41 volt. The threshold of MOSFET varies from 2 to 4 volts according to data-sheet. The op-amp should do a scale change so that the mid-value i.e zero error, should be scaled to threshold voltage.
I could not get any heating coil. I thought of buying nichrome wire and winding it to make a coil. In one shop, I found different types of bare wires, one looked like nichrome. But the shopkeeper refused to sell it to me. When he came to know the purpose of my purchase he thought that, I might meet with an accident and burn myself. I bought a heater from another shop but the coil cannot be used. It has a strange type of insulation it cannot be cut into pieces. To show the PID operation, now I am using an electric bulb. The heating / cooling rate is very slow. It is designed like that. Whereas, this project needs a set-up with very fast heating and cooling. But I am helpless. I am not finding any other alternative.
Today, I did the component testing. LM35 temperature sensor testing and calibration is yet to be done. Following figure shows the box heated up with a bulb. A digital thermometer to check the temperature. Components on the bread-board for testing.