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Topic: Increasing range on a 315Mhz transmitter (Read 263 times) previous topic - next topic

Fulliautomatix

Hi,

I'm using this keyfob transmitter....
https://www.adafruit.com/product/1095

And this receiver.....
https://www.adafruit.com/products/1096

And an arduino pro mini to control some DC motors.

Everything works fine except for one teensy problem - range. The manual says the range is "up to 25 ft" (about 7m) - I need a range of about 6 meter (so this ought to be fine) but in practice at 6 meters operations is intermittent and inconsistent.

What can I do do boost range - even by a little bit?

Despite what the manual says, the transmitter seems to use a PT2260 chip. the datasheet http://www.sc-tech.cn/PT2260.pdf say this operates between 1.8 and 10volts, and the keyfob contains two 3 volt CR2016 (6 volts in total) so was wondering if boosting this to the max of 10volts might make a difference?

Perhaps I should add some sort of short antenna? Would this help? if so where should it be connected?

Or is there a simple way of boosting the performance of the receiver?

To pre-empt any questions about why distance is so critical.... I'm using one keyfob to control two motors, and they have to be 12 meters apart, so I need to stand mid-way in-between the pair to control them both. Currently I need to walk a couple of meters to the left to control the left-hand motor, and then a couple of meters to the right to control the right hand motor. Ideally I'd like to be able to control them both without the need to move!

Thanks

jremington

Range is largely a function of antennas. At the very least both RX and TX should have 1/4 wave straight wire antennas (about 23 cm long for 315 MHz).

Fulliautomatix

Quote
At the very least both RX and TX should have 1/4 wave straight wire antennas
Ok, where should these go? I'm guessing I can just solder a short length of wire somewhere onto the keyfob transmitter?

thanks

jackrae

Adding a length of wire may detune the output stage if it's been optimised to suit the pcb track design and reduce the signal strength

It's an old trick that works with car key-fobs to increase effective range ;  Hold the keyfob to the end of your chin as you press the button. 

Fulliautomatix

Quote
Adding a length of wire may detune the output stage if it's been optimised to suit the pcb track design and reduce the signal strength
The receiver has coil of wire attached to it. Would it be best to straighten this out, or leave as a coil?

The transmitter-fob has no such wire. There is no obvious sign of any antenna etched into the pcb, assuming there isn't one (yet) then, with reference to the circuit diagram on the datasheet I linked to, where should the wire go?
thanks

Wawa

I'm using one keyfob to control two motors...
Sensitivity of those (433MHz) receivers is decreased with noise sources nearby.
Are there suppressor capacitors on the motor terminals.
Did you power the receiver from a "clean" source (not from the motor supply).
You can try if moving/pulling the receiver aerial coil out a bit helps.
Otherwise a home-made sleeve aerial might be the only option.
Leo..

DrAzzy

If I'm not mistaken, the RF portion of those is the garbage superregenerative design like the cheap green OOK receivers, just piped to that chip to decode it.

Those receivers are garbage (the problem is the receiver, not the transmitter - I tested a bunch of transmitters, and a bunch of receivers. The transmitters made much less difference than the receivers). Unfortunately, your boards have the receiver and the decoder integrated on the same board, so it's somewhat awkward to use a better receiver (like a superhet design based on, say, the Synoxo SYN470/SYN480 chip - as available on the RXB12 boards that sell for a buck or so on ebay).
ATtiny core for 841+1634+828 and x313/x4/x5/x61/x7/x8 series Board Manager:
http://drazzy.com/package_drazzy.com_index.json
ATtiny breakouts (some assembled), mosfets and awesome prototyping board in my store http://tindie.com/stores/DrAzzy

Fulliautomatix

Quote
Otherwise a home-made sleeve aerial might be the only option.
what part of the circuit should this be attached to?

Quote
Those receivers are garbage
This may be correct, but the problem (from my perspective) is only the range. the receiver/transmitter pair does everything I want up to about 4-5 meters range. Trying to persuade it work for a couple of meters more is the big problem!

Is there an alternative on the market? I'm looking for a 4 channel key-fob (or anything very small) transmitter and an arduino compatible receiver.


srnet

Or is there a simple way of boosting the performance of the receiver?
Probabbly not.

They are very likley designed to be very short range on purpose.
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

allanhurst

Several ways:

1/ more power.
2/ higher gain  ( directional ) antennas
3/ better receiver
4/ unobstructed path.

And...

Better coding techniques  ( low rate forward error correction with or without CDMA  )

LoRa devices use this last method to great effect.

Allan

Paul_KD7HB

When using the FOB, you are the antenna. So only solution is in the receiver. Better antenna or better receiver, or both.

Paul

Wawa

I think that replacing the pigtail aerail on the receiver with a DIY sleeve earial is the easiest solution.

Easilly made from a piece (~1.5m) of thin 50ohm coax (e.g. RG174U).

At one end of the cable, strip/remove ~30cm of the outer plastic.
Gently push the ground braid backwards over the cable.
For 315Mhz, trim the braid to 22.5cm and cut the core (with insulation intact) also to 22.5cm.
Push ~50cm of heatshrink over the whole lot, to keep thing where they are.

http://www.n4lcd.com/wireantennas/47-Vertical_Sleeve_Antenna_for_10m.jpg

Strip the other end of the cable ~2cm.
Solder core to the point of the removed pigtail, and braid to a ground nearby.

Hang the earial on a skyhook.
Leo..

jackrae

When using the FOB, you are the antenna. .....

Paul
That's probably why using my chin works - empty head acting as a resonator :)

DrAzzy

I suspect with concerted effort tracing out the circuit and cut+jumping, you could sever the connection to the RF portion of the existing receiver, and connect an RXB12 to it... It's ugly, but it would probably get you what you want.
ATtiny core for 841+1634+828 and x313/x4/x5/x61/x7/x8 series Board Manager:
http://drazzy.com/package_drazzy.com_index.json
ATtiny breakouts (some assembled), mosfets and awesome prototyping board in my store http://tindie.com/stores/DrAzzy

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