Simple RF T4 Receiver Supply Voltage

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argotwo
 
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Simple RF T4 Receiver Supply Voltage

Post by argotwo »

Hi adafruit

I am breadboarding a small mobile wireless remote project and have noticed that the receiver works fine with a regulated 5V supply but acts oddly when I tried to make the receiver portable by using two 3V button button-cells in series. I note the PT2272 chip has a wide voltage range (4-15VDC), but perhaps the RF section has less voltage tolerance?

So far I have only run the output to a LED, so there is a max of 10mA total supply current. I've measured my two-cell supply voltage and it doesn't appear to be going below 5.6V.

Any suggestions? I'm trying to keep my receiver box as small as possible as it is in my pocket with its job being to switch a relay for "push-to-talk", on a helmet mounted transmitter microphone (its for hangliding with the remote fob velcroed to my sleeve/cuff).

Cheers!

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Re: Simple RF T4 Receiver Supply Voltage

Post by adafruit_support_bill »

I've measured my two-cell supply voltage and it doesn't appear to be going below 5.6V.
Does the voltage drop at all when you activate the transmitter? Coin cells have a fairly high internal resistance and tend to sag a bit under load.

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Re: Simple RF T4 Receiver Supply Voltage

Post by argotwo »

Yes a little, from 6.2 to 5.6V.

I double-checked by going back to my first power supply which was a SMPS with an output of 5.1V, and the RX works again perfectly.

With the coin-cells the RX works fine with the TX very close to the RX, but step back a couple of feet and with one of the TX buttons pushed (and held) down, the RX output cycles on and off until brought back to very close proximity. I have two RXs and they both do exactly the same thing.

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Re: Simple RF T4 Receiver Supply Voltage

Post by adafruit_support_bill »

Measuring with a multimeter, you may be missing the worst of it. Most multimeters average readings over about 1/2 second or so. There may be momentary dips in the voltage that go lower than that. It might help to put a 1uF capacitor across the power and ground - close to the receiver.

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argotwo
 
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Re: Simple RF T4 Receiver Supply Voltage

Post by argotwo »

Yes I was thinking along the same lines :-)

Just to check, although the PCB has "+5V" printed on the board at the "+" pin, its ok to supply up to +10V? I see in the RX description in 'Shop' that the spec is: "simply power the receiver with 5-10VDC".

Many thanks.

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Re: Simple RF T4 Receiver Supply Voltage

Post by adafruit_support_bill »

Yes, up to 10v is fine.

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Re: Simple RF T4 Receiver Supply Voltage

Post by argotwo »

Hi Bill

Tried a 10uF that I had handy and no change. I ended up using a small 2S (7.4V) LiPo battery and this works fine, but still very strange previous behaviour.

In trying to squish the cct board in an enclosure as small as possible, in doing this I noticed the return of the toggling behaviour. I'm wondering now if the RF L/C design is simply not very tolerant of, well anything!

Thanks for your time on this :-)

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Re: Simple RF T4 Receiver Supply Voltage

Post by adafruit_support_bill »

I did some testing on one here and see similar behavior. It appears that the transmitter is re-transmitting the code repeatedly & the receiver drops out between transmissions - unless the signal is very strong. Since it is coded, I'm not sure why the signal strength should make a difference, but it appears that it does.

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Re: Simple RF T4 Receiver Supply Voltage

Post by argotwo »

Excellent that you saw similar behaviour - I'm not crazy then!

After a break of a day I went back down to my man-cave for another play and everything worked fine, even though the night before it was consistently toggling (!?!) I then realised the only thing I hadn't checked was the transmitter-fob batteries (coin-cells) and sure enough the volts were sagging probably because of its extensive use in testing previously. I'm guessing the overnight "rest" allowed the TX battery's to bounce back enough to provide a strong signal.

The learning from this - keep the TX (and RX) battery's fresh. Have to say though its not a good feature to have the RX output toggle when voltage is low. To state the obvious, far better that there is no output at all. Perhaps a design tweak needed?

PS: Did some googling research on Coin-Cells.Apparently after very little use they develop and internal resistance of up to 30 Ohms! The findings were that for any circuits drawing pulsed-peak currents the use of load-smoothing cap is almost mandatory. Exactly as per your advice previously :)

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