ACORN Inputs current/voltage specs

[Richards]

The ACORN User Guide for Acorn_rev3 states, page 7, lists the ON voltage to be between 0 and 5.9VDC and the OPERATING CURRENT to be between 17 and 22 mA.

When using a 2N2222 NPN transistor and a 100 ohm collector resistor to sink current, it looks like I'm getting close. The current is 17.4mA and the voltage is 1.8 VDC. Increasing the resistance to 220 ohms pulls 15.9 mA at 3.5 VDC. Going with more resistance increases the voltage and decreases the current. (The resistor from an Arduino to the base of the 2N2222 is not critical. I tried 2.2K to 10K base resistor with equally good results. The goal is to drive the transistor into saturation. A 2N2222 has a beta of 30 to 100 at ordinary currents, so the standard 4.7K to 10K often used with Arduinos do the job.)

Relay contacts allows the ACORN to pull a little over 18 mA, still within the specs.