This is a standalone board that takes eight 3V GPIO pins (such as from a MCP23017 or MCP23008 HAT board or just from eight of a Raspberry Pi’s GPIO pins and buffers them to drive up to eight LEDs from a 5V supply. It is specificly designed for common cathode signals. It has a ten position screw terminal at one end, for GND, GPIO 0 through 7, and +3V (it does not actually use the +3V connection, but includes it to match the terminals on a MCP23017 or MCP23008 HAT board and thus can support the use of ten conductor cable or pin header connectors, etc.). At the other end it is two sets of +5V and ground terminals (to allow for daisy chaining the +5V supply bus), and nine position screw terminal for LEDs 0 though 7 and the common cathode (K), which is ground.
Circuit Description
The circuit is just eight driver circuits, each featuring a NPN and a PNP transistor, that level shift and buffer the 3V logic to 20 milliamp, 5V LED drive circuits. The circuits include a current limiting series resistor, so there is no need to include external resistors on your LEDs. The circuit assumes 2V LEDs (typical of standard red, green, and yellow LEDs).
Parts List
| Value | Quantity | References | Mouser Part Number |
|---|---|---|---|
| MPQ6002 | 4 | Q1 Q2 Q3 Q4 | 610-MPQ6002 |
| 15K Ohms | 8 | R1 R5 R9 R13 R17 R21 R25 R29 | 603-CFR-25JR-5215K |
| 10K Ohms | 8 | R2 R6 R10 R14 R18 R22 R26 R30 | 603-CFR-25JR-5210K |
| 2K Ohms | 8 | R3 R7 R11 R15 R19 R23 R27 R31 | 603-CFR-25JR-522K |
| 150 Ohms | 8 | R4 R8 R12 R16 R20 R24 R28 R32 | 588-OK1515E-R52 |
| GPIO (3.3V) | 1 | T1 | 651-1725737 or 2x 651-1725685 |
| LED Power (5V) | 2 | T2 T4 | 651-1725656 |
| LEDs (Common Cathode) | 1 | T3 | 651-1725724 |
| Value | Quantity | References | Mouser Part Number |
Parts list for OctalLEDDriver boards. Mouser Project
The only parts that might be substituted are the screw terminal boards. Feel free to select either pin arrays or spring terminals for the terminals.
Circuit Board Layout
Board assembly is straight forward. You need to be careful orienting the quad transistors.
Downloadables
Full design information is available on GitHub here: https://github.com/RobertPHeller/RPi-RRCircuits/tree/master/OctalLEDDriverh.
This board is available on E-Bay at http://www.ebay.com/itm/132601805903?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1558.l2649.
