Voltage and current display

[TorqueRanger]

I am working on a constant current load like Dave's Jones design and I want to add a 2x16 led backlight display .. With the display I want to be able to see the voltage,current,and the total watts being generated .. I have never dealt with being a display like to known where to begin ?? I have read a couple display voltage and current articles  but I need the watts too so I don't overload  the heatsink  with too much heat..

[Richard Crowley]

That would seem like an ideal case for a microcontroller solution (Arduino, et.al.).  Pretty easy to measure voltage and current, calculate the power, temp, or whatever, and display the values on most any type of display(s).

[sleemanj]

I need the watts too so I don't overload  the heatsink  with too much heat

Firstly, Watts = volts multiplied by current, since you know both volts (use a voltage divider on the DUT input (DUT = Device Under Test) to get a value suitable to feed into an ADC on your micro controller) and current (measure the voltage at the top of your sense resistor(s) and calculate from it's known resistance using Ohm's law, then you can calculate the power the DUT is delivering.

Secondly, it is probably better to stick a thermistor on your heatsink (or the tab of the FET) and use that to get an actual reading of the temperature, you can use this to turn on a fan when it's "warm" and shut it down when it's "too hot", the values of which are up to you, and your datasheets.

If you have some spare op-amps (eg you've used a quad op-amp and have one or two left over) you can do the fan and shut down using those (use the op-amp as a comparator, with some hysteresis, calculate the voltages which will be present at your resistor+thermistor divider for the appropriate temperatures you want, and construct a set-point divider to match, feed the resistor+thermistor divider and the setpoint into your comparator, and use the output to drive a fet to turn on the fan, or to pull the gate of the main load FET low to shut it down).