Hi all. I have run into a bit of trouble with a sewable electronics project. I am trying to power a SparkFun 7-Segment Serial Display from one of the analog ports of a ATmega328 board. I realize this is unconventional, but I designed the circuit to not require any crossed connections to make the sewing a bit easier, and that was the only way to do it. The display wouldn't light up, and after some debugging with a multi-meter it turned out that the analog pin I was using (A3) was only at 1.3V despite a digitalWrite command. I tested the same command on one of the other analog pins (A0) and it produced 5V as expeced. When I bridge the VCC pin and A3, everything works fine. When I set A0 to 5V , and bridge it with A3, the output voltage drops to 1.8V relative to GND.
The really weird thing is that just running the exmple code from the sparkfun website without any modifications still somehow results in a ~1.2V reading from A3 to GND. I have no clue what is going on here. Usually I would disconnect the display from A3 and keep testing, but I am trying to avoid it. Troubleshooting is difficult as I had to clip the excess tails to prevent short circuits making me extremely reluctant to disconnect anything until I have figured out what the problem is, as the thread is very hard to work with, and it took the project on the order of 60 man-hours to get where it is. I was hoping someone here might know what is going on, or point me in the right direction.
Please post the code that you are actually using and a schematic of your circuit. How much current does the display require ?
Did the sketch and circuit work before you sewed it ?
You did test it, I hope...
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Thanks in advance for your cooperation.
If I understand you correctly, you're trying to power the display from an IO pin. IO pins can safely sink or source 20mA, I'm reasonably sure that your display uses more than that.
Further a complete port can safely sink or source 100 mA and the total current through the processor's Vcc and GND lines should not exceed 200 mA.
Number are for AVR based processors (2560, 328, ...).
sterretje:
If I understand you correctly, you're trying to power the display from an IO pin. IO pins can safely sink or source 20mA, I'm reasonably sure that your display uses more than that.
Further a complete port can safely sink or source 100 mA and the total current through the processor's Vcc and GND lines should not exceed 200 mA.
Number are for AVR based processors (2560, 328, ...).
The datasheet for the display says it's max draw is 14.1mA.
UKHeliBob:
Duplicate post deleted
Cross-posting is against the rules of the forum. The reason is that duplicate posts can waste the time of the people trying to help. Someone might spend 15 minutes (or more) writing a detailed answer on this topic, without knowing that someone else already did the same in the other topic.
Repeated cross-posting will result in a timeout from the forum.
In the future, please take some time to pick the forum board that best suits the topic of your question and then only post once to that forum board. This is basic forum etiquette, as explained in the sticky "How to use this forum - please read." post you will find at the top of every forum board. It contains a lot of other useful information. Please read it.
Thanks in advance for your cooperation.
For future reference, if I had a question about multiplexing displays, would that go in "LEDs and Multiplexing" or "Displays"?
whatwouldkantdo:
For future reference, if I had a question about multiplexing displays, would that go in "LEDs and Multiplexing" or "Displays"?
Whichever you feel most appropriate.
But not both.
If you feel you've made a mistake, you could always ask a mod to move it.
if I had a question about multiplexing displays, would that go in "LEDs and Multiplexing" or "Displays"?
Displays would seem to be the most appropriate of the two, but I would be inclined to put it in Programming if you have a problem with a sketch that you have already written or in Project Guidance if you need advice on selecting components. Both of those forum sections get more traffic than the subject matter sections of which I think that there are too many.
There are no hard and fast rules (nor can there be) apart from avoiding cross posting the same question in multiple forum sections.
UKHeliBob:
Please post the code that you are actually using and a schematic of your circuit. How much current does the display require ?
Did the sketch and circuit work before you sewed it ?
You did test it, I hope...
The code I am using is the example code for I2C linked in the post. The datasheet lists max-draw as 14.1mA.
0 -> Conductive Fabric Circle 4
1 -> Conductive Fabric Circle 1
2 -> Conductive Fabric Circle 3
3 -> Conductive Fabric Circle 2
4 -> Conductive Fabric Circle 5
5 -> LED 5
6 -> LED 2
9 -> LED 3
10 -> LED 1
11 -> LED 4
A1 -> Wire to fencing foil
A3 -> VCC on 7 segment
A4 / A5-> SDA/SCL respectively
Test the display current draw by powering it with 5V (not a port pin), with your multimeter on the current setting, in series with the Vcc connection. I have trouble believing the 14 mA specification.
How did you connect the display ground?