Michka Mélo, September 13th-14th, 2017

• FoAM's power supply does not go below 2.8 V of voltage.
• In order to control the voltage to a lower threshold, I built a resistor-based voltage divider.
• First version of the resistor-based voltage divider was made of a 100 ohms and a 10 ohms resistors in series. It worked but, smelled funny. After few runs, the 100 ohms had turned a nasty shade of black. It seems that the amount of current flowing in the resistor was too important because the resistor value was too low.
• The second version of the resistor-based voltage divider was made of a 2.2 kohms and 1 kohms resistors in series. No weird smells, it worked.
• However, I kept having funny results. I tested many of the components, and finally concluded with a test without the voltage divider that it might be perturbing the correct working of the circuit.
• I will therefore not present here the hectic results of these first tests.

• When powering the 1381E voltage detector directly with the power supply (power supply + pin on 1381E pin 2, power supply - pin on 1381E pin 3, we obtain a 2.8V voltage on its output pin (pin 1), which is the same value as the one measured between the + and - pins of the power supply.

• When connecting the BBC microbit 3V pin to the output pin of the 1381E (the GND pin of the BBC microbit being connected to the - pin of the power supply), the BBC microbit does not light up. The measured voltage on the output pin of the 1381E is 0.64 V.
• It seems that the 1381E does not supply enough current to its output pin to power the BBC microbit.

Explain why the second 2N3904 does not seem to light up. Tell the values of voltage drops

* Try out with higher