My BubbleDisplay project needed to control sixty DC motors or solenoids to control air injection into individual columns of liquid. Due to the large number of outputs needed, I am using a chain of (74HC595) serial shift registers so that three I/O pins can control all sixty outputs. As each serial shift register has 8 outputs, this requires eight chips (for a total of 64 outputs, four are unused). The 74HC595 can not source/sync enough current to drive the motors/solenoids directly, so I am using a TO-220 N-Channel MOSFET rated at 60 volts and 32 amps (digikey: FQP30N06L-ND) to drive the load, with an 1N4001 rectifier diode to handle current spikes. Because I had to make 8 (9 for a hot spare) copies of this circuit, I decided that fabricating a printed circuit board was the only way to go.
It only took me two tries (Moving from Version 1.0 to 1.1) before I was happy with the design, which you can see (populated for testing) above. Looks a lot nicer than the prototype, right?
I used the open source KiCad EDA software suite for the schematic capture and board layout and was quite happy with it. (Be sure to go through the Tutorial if you are just getting started!).
I am also posting my entire KiCad project directory in case you need to make changes:
The parts needed to populate (one) board (with digikey part numbers) are as follows. Listed prices are for quantities large enough to populate at least 8 boards:
1 74HC595 IC 8-BIT SHIFT REGISTER 16-DIP $0.63 digikey.com 296-1600-5-ND 1 CONN FEMALE 8POS .100" R/A GOLD $0.767 digikey.com S5483-ND 1 CONN HEADER 8POS .100 R/A 15AU $0.333 digikey.com 609-3321-ND 8 MOSFET N-CH 60V 32A TO-220 $0.94 digikey.com FQP30N06L-ND 8 1N4001 RECTIFIER 50V 1A DO-41 $0.1184 digikey.com 1N4001DICT-ND 8 RES MF 1/4W 10K OHM 1% AXIAL $0.0394 digikey.com S10KCACT-ND 8 LED SS 5MM 625NM RED DIFF $0.0932 digikey.com 754-1264-ND 8 RES 560 OHM 1/4W 5% CF MINI $0.0228 digikey.com S560QCT-ND
The right angle (R/A) headers allow you to daisy chain boards next to one another, but you could omit them and connect the boards using hook-up wire (not recommended for a large number of boards…) You may note that with the exception of the extra BATT + connection (allowing the MOSFETS to switch a voltage higher than logic level to the outputs) the connections are in the exact same order as SparkFun’s 74HC595 breakout boards so you can daisy chain them together. Although the 8 pin header has a BATT+ connection, if you are switching large currents you should also connect up the extra large GROUND and BATT+ pads with larger gauge wire. You could also NOT daisy chain the BAT+ connection and drive each board or set of boards from its own supply.