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i'm using nRF24L01+ units (with PA, LNA, and RP Antenna).  I have them connected to a barebones Uno (5V tolerant), with an MCP1700/33 regulating 3v3 power for the radio.  The datasheet says less than 120 mA peak 3v3 are needed to power the RF modules, but I seem to be having some inconsistencies in terms of power.  If i use an external 3v3 regulated power supply (i.e. 3v3 breadboard power) then the radios seem to work.  But, once I moved them onto the MCP1700's they don't seem to be reliable; missing ACK packets, some failed writes, etc.  From the RF24 debug statements it looks like the radios are working, and thus the regulator is working, but I'm still having problems in the connection.

I have the MCP1700 connected to a regulated 5V 700 mA power supply, with a 1uF ceramic cap across GND/Vin and another on GND/Vout, and I put a 0.1uF ceramic cap across VCC/GND at the module connector.

I think I should have enough power, as I've put an ampmeter in-line and the most I've seen pulled (when it's working using the 3v3 external supply) was 50-60 mA.

Any ideas what I might be doing wrong?  Something wrong with connecting the MCP1700's?  Something else I'm missing?

Thanks a lot
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I think I should have enough power, as I've put an ampmeter in-line and the most I've seen pulled (when it's working using the 3v3 external supply) was 50-60 mA.

Any ideas what I might be doing wrong?  Something wrong with connecting the MCP1700's?  Something else I'm missing?

Your problem is not the quantity of power available from your supply, but rather the quality.

In short, your power isn't clean enough. You can try adding some additional filtering  (an electrolytic, at least 10uF and maybe more -- up to 470uF, depending on how noisy your power supply is.)

The 1uF caps are consistent with the MCP1700 data sheet, so that should be fine. The 0.1uF across Vcc and Gnd near the module is also a good idea. Just add a nice fat filtering cap to reduce overall ripple and noise and see how that works.
 
Getting the power supply correct for the nRF2401+ modules is often the hardest part. When they are supplied correctly, they peform very well, but they like their power clean, clean, clean.

Let us know how you go.
 
« Last Edit: March 25, 2014, 04:18:22 am by pico » Logged

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In short, your power isn't clean enough. You can try adding some additional filtering  (an electrolytic, at least 10uF and maybe more -- up to 470uF, depending on how noisy your power supply is.)

Thank you very much.  After you mentioned this, I did a bit more research and found others making a similar recommendation.  I added a 100uF electrolytic cap to each unit (Vout to GND) and I now have my previously good units talking, as well as my new barebones (final hardware prototype) unit working which had never worked previously.

I'll now just need a bit more testing to see if i can drop the size of the cap, and finish my BOM.

Thanks again.
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