I'm trying to figure out how to make a nice power supply to the radio module HM-TRP.
I heard that running certain voltage regulators with capacitors having high ESR values is a bad idea and will cause instability.
For this reason I made the voltage supply setup to my circuit as follows:
The 7.2V battery powers everything and gives power to the 5V regulator LM2940.
Due to specs in the datasheet, I placed a 22uF electrolytic cap as close to the input and output of the LM2940 as possible.
then on the 5V side, I sprinkled a few 47nF ceramic capacitors throughout the board to reduce ESR and to give each section of the board better chances of a solid voltage. I have about a total of maybe 10 ceramics on-board (Its a large project).
Next, I have an LM1117 which the 5V feeds into in order to get a clean 3V output. It's ok if the output is between 2 and 3.9V. The output of that regulator currently has a 220uF electrolytic capacitor attached to it along with another 220uF (not shown) capacitor in parallel.
I then test my entire circuit out. Every single thing works beautifully, except for the radio module. I try running the thing with a speed of 38400bps and with the two wireless devices no farther apart than a meter.
When I run the test, for continuous wireless data communication, the data flow works nicely for about a few minutes, then the radio on my board stops working for roughly a minute, then it starts working again. and the process repeats. I did not create code in my microcontroller on-board that makes these delays happen. In fact, when the remote unit sends data to the on-board radio, the light must blink green. This light doesn't go on when the on-board radio stops working for the short time.
So I thought maybe its an issue with the ESR of the capacitors? So I tried replacing the second 220uF electrolytic capacitor with a 100nF ceramic capacitor. The results were maybe 1% improved but I still get that hiccup where the on-board radio module stops working for a period of time then works again.
Question is, is my voltage regulator setup? or could I use a better model number for either regulator?
And what about my capacitors? is my ESR out of valid range? or should I just go with a new kind of capacitors?