About 6 months ago I built a project with a Arduino Uno, MAX7219, DHT22 and a DS2302. I got it working great using a 9v external power supply connected to a femal barrel socket, with vcc to vin and gnd to gnd on the Arduino.
I have jst built the exact same project, but if I use a 9v power supply connected the same way as the other one, but the MAX7219 does not display any data, it just stays lit up. If use a 7.5v power supply, it works fine.
I have attached a picture of the wiring taken from outside, so I hope it is clear enough.
Thanks
a 9v power supply connected the same way as the other one
Two different 9V power supplies?
jremington:
Two different 9V power supplies?
Yes they are actually, and thought that 9v would be same in both???
The first one uses and works with a 9v supply , but the second one won't work with a 9v one, but will using a 7.5v supply.
I just find it strange that there is a difference, and would have thought that 9v would be fine for the second one.
Check the current capabilities of the power supplies.
The 9v supply used on the 1st project has a current rating of 3 amps while the other one for the 2nd project is 2.5 amps.
Those large LED arrays might be over-stressing the smaller power supply but then it would more likely flicker instead of lighting up.
2.5 vs 3.0 is a small difference in this context. Double-check your wiring. One way to do that is attempt to follow the wires and draw the schematic.
I found what the problem was because on the 2nd project, the MAX7219 stopped working. I then checked the voltages from the arduino to the breadboard, DHT22 and the MAX7219. When I used a 7.5v supply 7.5volts was coming from the 5v pin on the arduino, and consequently a 9v supply was giving 9v to the 5v pin from the vin pin????
Also the same voltage was going to the MAX7219 which probably cased it to fail. It lights up partially, but that's all it does now.
The arduino was or is a clone, and have now replaced it with a genuin Arduino Uno
Thanks for your input.
