# opt101 (photodiode) adjust voltage output

I'm using the popular OPT101 photodiode with 5V. How can I scale the output between 0 and 5V (or as close to that range as possible)? Now the output is ca 0-400mV (maximum is room light here).

I'm a noob, and if I had more experience, I would be able to figure out with >the datasheet< what Pin would lead to the desired 'amplification', but I have no clue where to start. I did follow the instructions outlined in the datasheet (pinned below), i.e. all recommended Pins are connected (Vs has 5V in that diagram, V- is connected to ground).

As far as I know, the circuit contains an opamp, that is probably usable to scale the output to the desired range, but I find no instructions about how to adjust it - I have a strong suspicion exactly one resistor or pin connection is needed to achieve this...

I should add, I was hoping I can achieve this without applying any negative voltage, since that seems a bit more complicated, and I avoided it wherever possible here

Circuit schematic from datasheet:

• To increase the output voltage you would need to increase the value of the 1 Mohm resistor, which is inside the IC so you cannot change it. There is no "amplification" pin. You will need a circuit to provide extra amplification, for example a "non inverting amplifier" that uses an opamp. Also you cannot get exactly 5 V output when your supply is also 5 V, so settle for slightly less than 5 V or use a higher supply voltage. Also, why do you need 5 V (instead of 400mV)? If you connect the voltage to an ADC maybe you can more easily change the ADC's range. Commented Oct 28, 2020 at 15:31
• That's the issue, I want to maximize the range of the ADC (that goes from 0 to 5 volts), anything that maximizes the output towards that range would, I guess, be beneficial in terms of having a better signal resolution Commented Oct 28, 2020 at 15:35
• Maybe you could disconnect pin 4 and not use the internal 1 Mohm resistor. Then connect a 5V / 0.4 V * 1 Mohm = 12.5 Mohm resistor between pins 2 and 5. Also put a 3 pF capacitor in parallel with that 12.5 Mohm resistor. Note that this might not work as expected due to the high value 12.5 Mohm resistor. But it is worth a try. What ADC are you using? For example the ADC in an Arduino can very easily be re-configured to a different voltage range. Commented Oct 28, 2020 at 15:35
• With a supply of 5 V the output of this IC can go only up to around 3.7 V, see table 6.5 "Voltage output, high" in the datasheet. So instead of 12.5 M ohm use a lower value. Commented Oct 28, 2020 at 15:39
• The ADC I'm using is basically an arduino. But essentially I just want to maximize the signal range from 0-5V from the sensor Commented Oct 28, 2020 at 15:49