RF reciever

computer guy

Can the propeller receive an RF signal on an input pin and respond accordingly.
This is for a robot.

Thank you

|-------|
|-------|----RF (((
|-PROP--|
|-------|-----------SERVO_1
|-------|-----------SERVO_2
|-------|

Post Edited (computer guy) : 5/9/2007 9:07:03 AM GMT

crgwbr

It can receive serial data from an RF transceiver, but I don't think you can just wire an antenna to an I/O pin and expect it to work. Also, could you be more specific in your questions?

Craig

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I would love to change the world, but they won't give me the source code

People say that if you play Microsoft CD's backwards, you hear satanic things, but that's nothing, because if you play them forwards, they install Windows.

I spent a minute looking at my own code by accident. I was thinking "What the heck is this guy doing?"

Mike Green

Since the Propeller is executing instructions about one every 50us, it can respond to pulses in the low RF range (maybe up to 3-5 MHz). The cog counters can certainly count pulses in the low to medium RF range (maybe up to 20-40MHz). It's not clear that this is what you really mean. The signal threshold is roughly 1.6V. Ideally, you'd want a logic high much closer to +3.3V and you'd want clean pulses.

computer guy

Ok, I want to get the propeller to recieve an RF signal either via just an aerial or via some form of circuitry.
The signal will come from a transmitter(RF aeroplane control) and the prop will respond to the signals by controlling servos.

Thank you

Leon

What frequency is the transmitter?

Leon





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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

computer guy

Havent gotten one yet.
What would you suggest?

Graham Stabler

All of the RC bands are above the 3-5Mhz range Mike mentions you would be talking somewhere between 27Mhz and 72Mhz.

The easiest solution is to tap the pulse position modulation (ppm) signal from a normal RC receiver, this is normally fairly easy to do, you just add a wire to one point on the circuit.

This page describes the signals sent to the servos and those received by the receiver that you can decode:

www.mp.ttu.ee/risto/rc/electronics/radio/signal.htm

Graham

Mike Green

If you're going to build the proper signal conditioning circuitry for the Prop to act as a receiver, you might as well buy a proper receiver. Most good receivers for the HF bands use at least one conversion to an IF frequency (usually 455KHz) and that would be decodable with a Prop if you really wanted to do it that way.

tellurian

Computer Guy,

I am not sure what you are after, but I have some working spin code for a Nordic nRF2401 tranciever module ...
see

http://store.qkits.com/moreinfo.cfm/TXRX24G

or

http://www.sparkfun.com/commerce/product_info.php?products_id=151

($13 at Qkits ... $22 at Sparkfun ... sheesh! I get them from Qkits, but I am sure the ones from Sparkfun ~must~ be better )

I love these things, complete monolithic RF trancievers antenna and all! They do all of the work for you, are highly addressable, and have quite good range! They are insane to debug though, so some working code will go a long way to help keep your sanity. They are perfect for robot telemetry and control for a bunch of reasons (see the data sheets for features). If you are interested let me know. I just got it working last night as part of a Propeller demo / presentation I am giving to a robotics club I am with. If you want it, give me a couple of days to package it up and submit it to the objects download section.

Allen

Opps, never mind ... I missed your post where you stated the signal will be via RF aeroplane control sorry.

Post Edited (tellurian) : 5/10/2007 4:16:26 PM GMT

JoeCreate

I've been using the XBee radios from Maxstream with the Propell on my iRobot Create. The radios are 3.3v 2.4Ghz with a TTL Serial interface. It connects directly to the propeller without any additional hardware, is about 1" square board with several antenna options, including a "chip" antenna on the XBee board itself. I use the FullDuplexSerial to do all of my debugging and remote control with it. By sending out VT52 (or whatever) formatting, hyperterminal works great for debugging and sending commands via keyboard. You'd want a couple of the XBee Pro's (about $30 each) for best range. I had ranges to almost a mile from atop a car with 3" external antenna to a handheld looking down the street full of traffic with a 1" antenna.

crgwbr

JoeCreate said...
...It connects directly to the propeller without any additional hardware...

I hope you put a couple resistors on the rx/tx lines. The prop can't take a 5v signal directly. (I've learned that the hard way )

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I would love to change the world, but they won't give me the source code

People say that if you play Microsoft CD's backwards, you hear satanic things, but that's nothing, because if you play them forwards, they install Windows.

I spent a minute looking at my own code by accident. I was thinking "What the heck is this guy doing?"

Mike Green

crgwbr,
Notice that JoeCreate said "The radios are 3.3v 2.4Ghz with a TTL Serial interface". They do connect directly to the Prop since they're 3.3V devices. They don't need protective series resistors. Sometimes these (and a few other 3.3V parts) are bought with a 5V interface like the PING or the HM55B compass or Selmaware's xBee AppMod. These do require the series resistors to protect the Prop from the possible 5V logic level.

computer guy

So do i have this right.

If i get an RF airoplane controller and an XBee transiever the XBee will be able to revieve the signal from the RF controller and respond acordingly.

Thank you

simonl

Nope! To use the aeroplane RF you will need the transmitter AND the receiver.

You have several options for what you're attempting:

1. Using the aero' Tx/Rx:

a) Wire each servo channel from the Rx to the PChip; 'read' the pulse width (usually between 750ms & 2100ms); do something with the data!

or

b) Tap into the Rx to get the actual RF signal stream; wire that to the PChip; interpret the stream (different between manufacturers); do something with it

2. Create your own Tx/Rx pair with (say) a Nordic nRF2401 or Maxstream XBee; you decide what data gets sent/received

Personally I've already used method 1.a) - very simple to get working, and I already had the Tx/Rx.

I'm now about to start with option 2, as I have a need to pass data in BOTH directions.

HTH.

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Cheers,

Simon

BTW: I type as I'm thinking, so please don't take any offense at my writing style

---

www.norfolkhelicopterclub.co.uk
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again ;-)

computer guy

So if i got 2 XBee units and used one of them on the robot and the other as a remote.

Is it alright if the controller uses a BS2 and robot uses a Prop or would the timing be out of sync.

Thank you

simonl

Shouldn't be any timing problems - baud rates should be set according to capability, and RF (over air) timing is handled by the XBee. Not sure about buffering though - I'd start testing with a low baud rate, then build up from there.

Don't know much about the BS2, but think you'll need to watch voltage levels (BS2=5V?, PChip=3.3V)

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Cheers,

Simon

BTW: I type as I'm thinking, so please don't take any offense at my writing style

---

www.norfolkhelicopterclub.co.uk
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again ;-)

computer guy

Thanks for the advice will get working on it strait away.

Thank you

Mike Green

Martin Hebel (www.selmaware.com) sells adapters for xBee transceivers for the Stamp (and the Prop). One's an AppMod and plugs right into a BOE. Consider getting the "pro" version (xBee-Pro) which takes more power, but has more range. Both versions plug into the same socket and work identically (except for power and range).

simonl

Yup, forgot to mention that the XBee (& XBee-Pro) has a wierd pin-out spec - I think it's 2mm pitch - so won't fit directly into a breakout board. An alternative to the one Mike's pointed out is at Sparkfun (http://www.sparkfun.com/commerce/product_info.php?products_id=8276). Don't forget to get the SIL headers with it!

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Cheers,

Simon

BTW: I type as I'm thinking, so please don't take any offense at my writing style

---

www.norfolkhelicopterclub.co.uk
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again ;-)

JoeCreate

simonl said...
Shouldn't be any timing problems - baud rates should be set according to capability, and RF (over air) timing is handled by the XBee. Not sure about buffering though - I'd start testing with a low baud rate, then build up from there.

Don't know much about the BS2, but think you'll need to watch voltage levels (BS2=5V?, PChip=3.3V)

There is a setting on the XBee to tell it how many characters to buffer before transmitting.· I set it to 0 for real-time transmission.

The pinout spacing is certainly a pain on the XBee's.· You only need 4 pins so worst-case they could be wire-wrapped (does anyone do that anymore?)· I had to get a board made to be able to interface it with my own stuff.· ExpressPCB.com ...· Here is the board I had printed to get things started.

I don't design boards as a profession, expecially RF related boards, so feel free to point out any glaring no-no's.

Post Edited (JoeCreate) : 5/11/2007 3:49:29 PM GMT

Graham Stabler

Personally I think that if you want RC type controls you should stick with an RC transmitter and follow Simonl's suggestion 1b which is also what I suggested. Its very easy to decode the PPM signals and they only vary in polarity between manufacturer.

Otherwise as well as sorting out the software you have to build a transmitter with sticks and all that entails.

If for any reason you really did feel you needed to use a zigbee or similar then you could interface with an RC transmitter through its buddy port, the transmitter transmitts nothing (you remove the crystal) but supplies the PPM signal directly through the buddy lead that way you could have a mixture of RC type control and anything else you wanted through the same RF channel.

Graham

computer guy

I liked the 2 zigbee idea because of being able to have an lcd on the reciever.

Thank you

JoeCreate

computer guy said...
I liked the 2 zigbee idea because of being able to have an lcd on the reciever.

Thank you

Hey, if you really used the zigbee protocol, then if the plane got out-of-range, you·could send-up another to relay commands.· Or, send up another to pickup the signal from the plane that got out of range·and relay to you the gps coordinates for the SAR team.

You can get the RSSI value out of the XBee's so both sides can know when you are getting too far away from eachother.

computer guy

You have a point there.
Another great reason to go with the zigbee units.
I really like this idea and think i will stick with it.

Thank you

computer guy

Have gone with the zigbee pro and a small enclosure.

Post Edited (computer guy) : 5/26/2007 7:57:00 AM GMT

computer guy

Hey computer guy,

Hey i am talking to myself.

Bump

M. K. Borri

I use the Xbee for NAVCOM AI, this way I can pretty much treat the signal as a normal serial communication.

computer guy

What is NAVCOM AI?

computer guy

Just moving this to page 2:

Hey could the propeller read a USB signal.
I'm thinking wireless XBox controller.

Thank you

M. K. Borri

NAVCOM AI is my universal navigation/communication project, see here http://forums.parallax.com/showthread.php?p=650217



Thing is -- the Prop probably can do that if you dedicate a cog to it (the Prop can do just about any damn thing if you dedicate a cog to it, I think...). The real question is how much of the receiving do you want to do by software?

Ultimately when it comes to RF, your best solution depends on:

1- What's your max. intended range?
2- What's your bandwidth? As in, how many (effective) bits per seconds do you want to send?
3- Is it 1-way or 2-way?

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http://forums.parallax.com/showthread.php?p=650217

meow, i have my own topic now? (sorta)

hkimball

i may have missed somethingsomewhere in this post, but the xbee has a very limited range, only 300' line of sight
you may want to look at a different radio from maxstream if you want your plane to be any real distance from you