How to output a true analog voltage at output pin
You basically have three options:
- Switch to an Arduino Due which has a built-in DAC which outputs a real voltage.
- Add an external DAC chip (such as the MCP4821/2) to create the voltage for you
- Use a low-pass filter (R-C network) on a PWM pin.
Of the three options I usually use an MCP4822 since it gives the best results and doesn't cost as much as using a Due.
At 5V, a 1 ohm resistor will try to sink 1A and far exceed the 40mA specs. Please use at least a 5/0.040=125 ohm resistor to protect your pin. And if you put the a capacitor between your resistor and ground, the RC circuit of the capacitor will smooth out the PWM into an analog voltage.
Please try the suggested @russell answer with a 47K resistor and 1uF capacitor, you will get an analog voltage at the junction to use with your electronic load.
As far as I know Arduinos have ADC (Analog to Digital Converters) but do not have any DAC (Digital to Analog Converters). So you can not output a set voltage from any pins based on a digital value.