The TIP120 Arduino shield

  This article is about a homemade Arduino shield, using a TIP120. The TIP120 is a darlington transistor that works as an electronic switch, it can handle large power, such as 60 Volt, 5 Amp (for high power you should use an aluminum cooler). This approach has some advantages over a relay circuit, and some disadvantages too, as you all can imagine, one of the disadvantages is the use of 110/220V circuitry as the TIP only works with 60V, on the other hand you can use PWM on it, it is faster than a mechanic switch as the relay and I imagine it consumes lower power on switching than the relay.
I used the circuit on the right (which I found somewhere over the internet) to build a schematic as you can see on the image at the
right to build afterwards an Arduino shield.


At the top of the image we see the TIP and the Arduino connection, the Arduino signal (that can be a regular digital output with an on/off behavior, or a PWM digital output to provide dimming on a lamp/LED or motor) and the GND provided by the Arduino board. On the lower end of the schematic we have 2 board connectors, one for connecting the load with the polarity showed (the polarity is only important on devices which have one, in case of a DC motor the TIP is protected by a diode 1N4007 or similar) and the other to connect the power. The 1 k Ohm resistor should be replaced by a 4k7 because of ground fluctuations.
The final result can be seen in the pictures.



NOTE: Has been registered a situation where the input control pin had a fluctuating voltage and the load and power were connected leading the TIP to a ON false situation, a workaround could be increase the resistor value or ground the control pin. Not tested yet.