This is my first use of transistors in a project. I need to control a SainSmart 16-Channel Relay Module using an Arduino 101(3v3 GPIOs). This Relay Module uses 5 vdc through Opto couplers to power the relays. The input pins on the relay board are at 4.4 vdc and need to be brought to GND to switch on.

When I connected the Arduino 101(3v3 GPIOs) directly to the relay module some of the relays would stay on while others would be controlled by the Arduino. It all worked fine when I tried an Arduino UNO(5v GPIOs) in place of the 101. But, I want to use the BLE capabilities of the 101.

So my solution is to use  2N22222N2222 transistors because I’ve read they are good at general purpose low-mid power switching Below is the configuration I think is correct Any feed back would be greatly appreciated I’ve tried reading the Data Sheet but I’m mostly going off of other forum posts


Relay Board inputs; +4.4vdc, input to ground 4mA

Arduino 101; 3.3vdc GPIOs, max 20mA per GPIO

T1  2N22222N2222

R1: 10K, to reduce current through the Base to 0.33 mA

R2: 100K, drop down resistor. (is it needed?)