Click to enlarge If you’ve been reading my articles (1, 2) on the Mindsensors PCF8574A board but are unable to purchase one for any number of reasons, here’s a blatant clone made on a breadboard.  It will function pretty much the same way as the Real Thing but doesn’t look nearly as nice.  Below you will find the schematic and the values of the components. The +5V’s in the circuit are all hooked up to pin 4 on the NXT connector.  Pin 1 on the connector is not connected to anything, it’s the analogue input for the NXT and we’re using I2C.  On the Mindsensors board C1 is a 22uF capacitor, however, I only had a 47uF.  I guess either will be fine.  Here is some source code to check if you’ve hooked it up properly: LINK.  It should blink the LED a few times a second.  The breadboard adapter is a home made one.  For instructions and more photos of that, click here.

Click to enlarge

R1, R2 82KOhm
R3 1KOhm
D1 10mA red LED
C1 47uF
C2 0.1uF