hi folks,
working on something: it's a Seven Segment display, make with 10mm LEDs, driven by an Arduino.
So far so good.
The LEDs are in fact 3 x LED in serial, with a current limiting resistor, connected to ground. These are going to be powered from a 12 V source (no choice; LED are 3.2V x 3 = 9.6V), so I figure out that I would need to drive them from a transistor, even better a transistor array.
I then made a PCB, ordered a bunch of them and then ...Crap ! I screwed up on the orientation of the LEDs and pinout vs the selected transistor array.
No problem; I'll just make a small board, with transistor and reuse my main board - which I did
![custom board.JPG custom board.JPG](https://maker.pro/forums/data/attachments/27/27608-1aec71cd00313cebb36c564981edd479.jpg)
Problem is that when I install the custom board, all the LEDs are lit !!! Checked the output of the Arduino: 0V but the **** LEds are ON !
I tested my board on a proto-board
![test setup.JPG test setup.JPG](https://maker.pro/forums/data/attachments/27/27609-6225b03840c5a663a4bca79d96002551.jpg)
When I apply 5v to the base, it works ! 0 volt, they turn OFF
What am I missing ?!?!
working on something: it's a Seven Segment display, make with 10mm LEDs, driven by an Arduino.
So far so good.
The LEDs are in fact 3 x LED in serial, with a current limiting resistor, connected to ground. These are going to be powered from a 12 V source (no choice; LED are 3.2V x 3 = 9.6V), so I figure out that I would need to drive them from a transistor, even better a transistor array.
![main circuit.JPG main circuit.JPG](https://maker.pro/forums/data/attachments/27/27607-2cfefc4ab70adb07a24f288dd50f8e53.jpg)
I then made a PCB, ordered a bunch of them and then ...Crap ! I screwed up on the orientation of the LEDs and pinout vs the selected transistor array.
No problem; I'll just make a small board, with transistor and reuse my main board - which I did
![custom board.JPG custom board.JPG](https://maker.pro/forums/data/attachments/27/27608-1aec71cd00313cebb36c564981edd479.jpg)
Problem is that when I install the custom board, all the LEDs are lit !!! Checked the output of the Arduino: 0V but the **** LEds are ON !
I tested my board on a proto-board
![test setup.JPG test setup.JPG](https://maker.pro/forums/data/attachments/27/27609-6225b03840c5a663a4bca79d96002551.jpg)
When I apply 5v to the base, it works ! 0 volt, they turn OFF
What am I missing ?!?!