HIGH CURRENT DC DEVICES TIP122

  


The Controlling Multiple LEDs Tutorial uses the 2N3904 small current transistor. This works well for controlling additional relatively small current devices with the Arduino. You may want to use the Arduino to control a DC powered device that draws more current that the 2N3904 transistor can supply. A solution for this situation is to use an NPN Darlington Transistor designed for medium power linear switching applications. In this tutorial we will use a TIP122 transistor, which can power devices up to 100VDC at 5 Amps. This can be used to power devices such as motors, solenoids and fans, where the only necessary operation control operation is ON and OFF (see the H-Bridge Tutorial for bi-directional rotation and speed control of DC motors.)

The circuit is identical to the 2N3904 transistor circuit - the base of the transistor (PIN 1) is connected to the Arduino output pin (D6) through a 1K OHM resistor. The emitter (PIN3) is connected to ground and the collector (PIN2) is connected to one end of the coil of the device being driven (in our example we have a 12VDC Solenoid connected). The other end of the coil is connected to the +12VDC external power supply (the ground from this power supply is connected to a common ground with the Arduino - this is necessary for the transistor to function). It is very important to put a diode across the coil of the device being powered to protect the control circuit from a potential voltage spike that can be created when current is released from the device being powered.

The digital voltmeter ICL7107CPL

Here is my lovingly-crafted schematic for the voltmeter module. Note that this could be made as a standalone voltmeter, it will measure up to 20v DC. In our finished product, the +5V will be sourced from an LM78L05 voltage regulator.

And the parts list:

    IC1 – Intersil ICL7107CPLZ
    IC2 – Intersil ICL7660
    D1~D3 – 1N4148 diodes
    LED displays – Agilent HDSP521G 2 x 7-segment green displays (common anode). You can use anything really, as long as it is common anode, and each segment is ~8mA
    R1 – 220 ohm – all resistors 0.25W
    R2 – 10k ohm
    R3 – 1M ohm
    R4 – 47k ohm
    R5 – 15k ohm
    R6 – 100k ohm
    R7 – 1k ohm multiturn potentiometer/trimpot (for calibration)
    C1 – 10nF – all capacitors must be rated for at least 25V
    C2 – 20nF
    C3 – 470 nF
    C4 – 100 nF
    C5 – 100 pF
    C6,7 – 10 uF electrolytic

Please note that this is a work in progress and errors may have been made, or values altered at any time after publication.