Hello.
I am pretty new to the world of Arduino and circuits in general, but I have this on my hands:
I have an ATMEL ATMEGA 168-20PU chip, which has the Arduino bootloader burned and I program it with Arduino sketches successfully via an external FTDI converter chip. I have also wired 10 digits of a seven-segment-display. I have their individual segments (A, B, C, D and so on) wired together, and I have their common anode to control with the arduino. So instead of having around 80 pins to control (each for its individual segment), I just have 18 (10 for the common anode control and 8 for the segments). I did want to do "matrixing" or "multiplexing" (however that is called) to drive the digits on the display one by one very fast, but I ended up having the segments lighting up very dimly. And now I think that this setup is wanting too much current. Can you do some calculations for me, or suggest some kind of transistor? I really do not know how these things work, so thank you in advance.
You need to control PNP transistors (or logic level, low Rds P-channel MOSFETS) to drive current into each anode.
Then buffer the individual cathodes with ULN2803, or TPIC6B595 shift register, so that full 20mA can be sunk thru each segment.
Your coding is also important - need to maximize the on-time for each digit.
Thanks very much. I just have one question: for what current should the PNP transistors I get be rated at?
an external FTDI converter chip.
I'm just curious. Which chip ?
So instead of having around 80 pins to control (each for its individual segment), I just have 18 (10 for the common anode control and 8 for the segments). I did want to do "matrixing" or "multiplexing" (however that is called) to drive the digits on the display one by one very fast, but I ended up having the segments lighting up very dimly. And now I think that this setup is wanting too much current. Can you do some calculations for me, or suggest some kind of transistor? I really do not know how these things work, so thank you in advance.
thank you in advance.
Unfortunately ,it's not in advance, but rather after the fact. You could have saved yourself a lot of grief if you had consulted us at the first sign of trouble ..
Crossroads has helped a lot of members with LED 7-segment multiplexing circuits and he could have steered you back on track.
Which reminds me...
@Crossroads,
Whatever happened with CancunManny (and his son) ? Did he ever get the circuit working ? I'm been holding my breath for so long I'm turning blue in the face....
pnp, 200mA is good.
CrossRoads:
pnp, 200mA is good.
Thanks very much! I will post after I get the parts.
raschemmel:
an external FTDI converter chip.
I'm just curious. Which chip ?
FTDI FT232RL chip on a breakout board.
I haven't heard from cancunmanny in a while, he was still assembling last I knew.