These are a must for driving any circuits over 20mA.  TTL logic outputs from the OOPic or basic stamp, PIC, etc do not have the capacity to drive much more than an LED.  These boards allow you to easily drive higher current devices.  It will drive up to 50V and 2 watts of power (1 watt per channel, but the channels can be paralleled for over 1 watt).  The circuit can handle about 500mA continuously.  The circuit also has inductive load transient suppression which occurs when driving such things as coils on relays. 

All our high current drivers have 7 channels.  All but the basic assembled board and one relay board have status LEDs which will light with a TTL (+5VDC) logic input.  The boards that have relays are rated at 10A@120VAC.    An external power source is plugged into the board that drives the loads. If you use the relays, then the supply needs to be either  5VDC or 12VDC.  The 5VDC coils will draw about 60mA each.  The 12VDC coils will draw about 37mA each. 

If you want screw terminals as pictured, you can select that addition, else you can solder your wires right into the holes on the PCB.