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'[OT]: RF Transmitter, Receiver'
2002\06\24@130315 by Anand Dhuru

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Folks, I need a transmitter, receiver to integrate in a product, where the range required is minimal (not more that 10 feet). Also, the bandwidth requirement is exremely minimal; a few bytes to be sent every few minutes.

The criticality is more to do with the economics involved. I cant therefore think of using pre-assembled rf modules like the Ming series.

Considering the modest range and bandwidth requirements, I am tempted to use my own receiver and transmitter, integrated on the PIC PCB, for the project.

Are there any 300 MHz or 418 MHz circuits on the internet to do this? I have the circuit for the transmitter, which is extremely simple in design, and I'm hoping someone can help with the receiver schematic.

Thanks and regards,

Anand Dhuru

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2002\06\24@131145 by adam

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Hi Anand,

The first thing I would do, given your low power requirements, is check
out the rfPIC series.  I've never used them because of their low TX
power capabilities (somewhere around 2 dbm if I remember correctly), but
they're probably your best bet.

You're right, the TX circuits are much simpler.  For a possible RX
solution you might want to check out MICRF001BM.  I haven't priced them
in a while but I think they're somewhere around $5 in low quanities
(once again, not sure though).

Is this a one-way thing or do you need transceivers?

Regards,
Adam Smith

> {Original Message removed}

2002\06\24@160944 by hard Prosser

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Take a look at super-regenerative receivers.
I'mthinking of  a similar project at the moment & am considering a simple
regen circuit. The advantages are that I'm hoping to be able to use the
same components for both TX & RX and possibly a single port pin (changed
between an output and an input).
"Electronics & Wireless World" had an article on superregens a month or so
back & the circuits given appear to work OK at 70MHz or so - I've just got
to get the right transistors for UHF operation.

The disadvantage is that unless you buy a resonator to control the
frequency it could be difficult to tune & temperature drift could be a
problem - and with a resonator the bit rate is somewhat limited.
If you're interested I'll try and draw a rough circuit. - Probably only one
or two transistors but there could be a software requirement to process the
received signal unless additional external components are added.

Richard P




Folks, I need a transmitter, receiver to integrate in a product, where the
range required is minimal (not more that 10 feet). Also, the bandwidth
requirement is exremely minimal; a few bytes to be sent every few minutes.

The criticality is more to do with the economics involved. I cant therefore
think of using pre-assembled rf modules like the Ming series.

Considering the modest range and bandwidth requirements, I am tempted to
use my own receiver and transmitter, integrated on the PIC PCB, for the
project.

Are there any 300 MHz or 418 MHz circuits on the internet to do this? I
have the circuit for the transmitter, which is extremely simple in design,
and I'm hoping someone can help with the receiver schematic.

Thanks and regards,

Anand Dhuru

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2002\06\24@162420 by Brendan Moran

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Well, I don't know about him, but I'm interested.  I've been looking at R/C
for years, but never gotten anything together, paritally because of the
price per control channel.  Having a PIC send UART burst transmissions
through an RF transmitter on the unliscenssed band sounds like a great plan
to me.

If it weren't for the cost, I'd almost think that using 802.11 would be a
nifty way of controlling R/C type devices, but the interface and the base
cost would make that idea prohibitive: it's cheaper to do the same thing
with a conventional R/C controller.

--Brendan
{Original Message removed}

2002\06\24@170424 by IvanEamus

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Hi,
I don't recomend using seo for tx, freq stability would not be good. Also
super regen ccts do work and can be sensitive, but care is needed to stop
radiating "hash". Good luck.

Ivan

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2002\06\24@172056 by hard Prosser

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Yes - I forgot to mention the interference problem as for only 10ft of
transmission distance the power levels can be kept very small - and the
receiver current can be minimised reducing its spurious outputs to quite a
low level. (As per the "Electronics World" article)

Richard P




Hi,
I don't recomend using seo for tx, freq stability would not be good. Also
super regen ccts do work and can be sensitive, but care is needed to stop
radiating "hash". Good luck.

Ivan

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2002\06\24@175856 by hard Prosser

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part 1 1893 bytes content-type:text/plain; charset=us-ascii

OK - Here's the circuit so far - Setup for about 22MHz as the transistor is
only a 2N2222

L2 and C4 basically determine the frequency, with some help from C1 & C2.

In RX mode an approx 20kHz pulse train appears at the output with about
2.1V to 3.0 V range.  The actual pulse frequency depends on the received
feild strength in a roughly logrithmic relationship.
So, the PIC has only to count the number of pulses in a given interval - or
measure the time for a number of pulses and it should be able to figure out
if there is a signal being received (i.e. it maintains a record of the
timing under idle condition and looks for a change).

Under TX, the PIC pin changes to output and pulls low. This changes the
bias conditions and removes the super-regen effect, turning the circuit
into an oscillator.
For short ranges, this can be sufficient (I hope) to be regarded as a
transmitter.
Modulation by manchester coding should be OK to pass data at a few
kbits/sec - depending on range etc. required.

A small aerial connected to Q1 Collector appears to assist reception.

Note: this circuit is copied from a working PSpice simulation. I have used
the same basic circuit but with component values altered & a better
transistor at about 70MHz but have not yet tried making 2 of them &
connecting to PICs for communication.

One area of possible difficulty is that according to the simulation, the RX
frequency is centred at about 22MHz, while the TX frequency is about 1MHz
higher. Possibly a better transistor would reduce this effect.

As with most minimal component circuits, there is a fair amount of
interaction between components and frequency, sensitivity etc. but it may
serve as a starting point for someone.
If anyone does play with it I'd be interested to hear of the results.

Enjoy

Richard P

(See attached file: superregen.jpg)

(See attached file: superregen.jpg)

part 2 16069 bytes content-type:image/jpeg; (decode)


part 3 136 bytes
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2002\06\24@182037 by Brendan Moran

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I have a fair number of 2N5179s (metal can package, with can grounding
lead)kicking around--they're rated for up to 1GHz--I think they'll make a
suitable transistor for the job, might even make it up into the unliscenced
band, and therefore not have to worry about FCC people in their white vans
comming to find me if I try for slightly higher power.

I'm afraid that I'm fairly new to RF, and I have virtually no experience
with transciever circuits.  Though I've wanted to play with R/C for years,
I've never actually buckled down and figured out what I need to do it.

Is the 500nH coil is the actual tranmission element?  Is there any way of
amplifying the ouput to get a longer range capability?  If so, is there any
way of amplifying the input as well?

Am I looking at the wrong kind of circuitry to do what I want to do? (i.e.
R/C via a PIC)

I think I'll go hunt through the PICList archives for a while.  There's
probably been many discussions on this subject before.


{Original Message removed}

2002\06\24@184242 by hard Prosser

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Yes - I guess the "500nH" coil is the main radiator if there is no antennae
attached - but even a small length of wire on the collector of the
transistor appeared to increase the RX range considerably.
You would need to be careful if looking for greater range however as the
frequency control would be pretty poor. As far as amplifying the TX or RX
side is concerned it could be done - but at the expense of the
bi-directional nature of the circuit. An RF amplifier stage for TX would
kill the RX performance etc. You might get higher output by reducing R4
somewhat. A PIC pin can sink about 20mA so 120ohms or so would be about the
minimum reccomended.

Or you could switch an amplifier in but for this level of complexity you
would be better off with something better to start with.

The 2N5179s should be fine.

I've also looked at basing the circuit around a Hartly oscillator. This has
the advantage of providing a certain amount of neutralisation for the
collector-base capacitance.and might allow lower spec xtors to operate at
higher frequencies. I have had 2N2222s / BC547s oscillating at 400MHz or so
- but no joy with the super-regen side of things.

Richard P




I have a fair number of 2N5179s (metal can package, with can grounding
lead)kicking around--they're rated for up to 1GHz--I think they'll make a
suitable transistor for the job, might even make it up into the unliscenced
band, and therefore not have to worry about FCC people in their white vans
comming to find me if I try for slightly higher power.

I'm afraid that I'm fairly new to RF, and I have virtually no experience
with transciever circuits.  Though I've wanted to play with R/C for years,
I've never actually buckled down and figured out what I need to do it.

Is the 500nH coil is the actual tranmission element?  Is there any way of
amplifying the ouput to get a longer range capability?  If so, is there any
way of amplifying the input as well?

Am I looking at the wrong kind of circuitry to do what I want to do? (i.e.
R/C via a PIC)

I think I'll go hunt through the PICList archives for a while.  There's
probably been many discussions on this subject before.






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2002\06\24@185445 by Brendan Moran

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----- Original Message -----
From: "Richard Prosser" <spamBeGoneRichard.ProsserspamBeGonespamENERGY.INVENSYS.COM>
To: <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
Sent: Monday, June 24, 2002 3:41 PM
Subject: Re: [OT]: RF Transmitter, Receiver

> Or you could switch an amplifier in but for this level of complexity you
> would be better off with something better to start with.

That's usually the way it works.  When you start trying to improve
range/sensitivity/frequency of anything, you tend to lose the simple
circuitry ;)

> The 2N5179s should be fine.

I hoped I'd find a good use for those--I didn't think it was really fair to
them, being such nice HF transistors to use them whenever I needed a generic
NPN ;)

> I've also looked at basing the circuit around a Hartly oscillator. This
has
> the advantage of providing a certain amount of neutralisation for the
> collector-base capacitance.and might allow lower spec xtors to operate at
> higher frequencies. I have had 2N2222s / BC547s oscillating at 400MHz or
so
> - but no joy with the super-regen side of things.

If it's Miller capacitance that's the problem, why not use a cascode
configuration?  Hold the collector of the first transistor at a constant
voltage with a second transistor, and thus eliminate the effect of the
inherent capacitance.

It's a common emitter input, common base output circuit.  I think they work
fairly well at eliminating Miller capacitance.

Though, I don't actually know if that configuration would correct the
problem in question, but I'd think that it would be worth a shot, at least.
I'll have to try this stuff out.

Thanks for the suggestions!

Regards,
--Brendan

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2002\06\25@074657 by Russell McMahon

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Must it be RF?
Infra Red will cover this range easily provided there are not problems with
optical line of sight.
At 10 feet you can point the transmitting LED in almost any direction
indoors and still get "copy".
38 kHz receivers (or thereabouts) are available as integrated 3 lead devices
complete with lense and the transmitter is as little as an IR LED and a
resistor and possibly a transistor and another resistor.

       RM



> Folks, I need a transmitter, receiver to integrate in a product, where the
range required is minimal (not more that 10 feet). Also, the bandwidth
requirement is exremely minimal; a few bytes to be sent every few minutes.

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2002\06\25@081439 by Anand Dhuru

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Thanks Adam, Richard, Brendan, for your helpful inputs.

I'll try Richard's superhet circuit.

> The first thing I would do, given your low power requirements, is check
> out the rfPIC series.  I've never used them because of their low TX
> power capabilities (somewhere around 2 dbm if I remember correctly), but
> they're probably your best bet.
>
This did look the most tempting, but I thoght that Microchip just have a
transmitter in the RF-PIC range (RF12C509 AG/AF). If they do have a
receiver, and it is available now, that would be the simplest (and most
compact) solution.

> You're right, the TX circuits are much simpler.  For a possible RX
> solution you might want to check out MICRF001BM.  I haven't priced them
> in a while but I think they're somewhere around $5 in low quanities
> (once again, not sure though).

A great product, at a great price; I am checking up the availabilty of
Micrel products here in India.

>
> Is this a one-way thing or do you need transceivers?

It is a one-way app, I do not need transcievers. The transmitter would be
battery operated (in a key-fob), and the receiver would work off a vehicle's
battery.



> Regards,
> Adam Smith
>
> > {Original Message removed}

2002\06\25@105347 by Roman Black

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Very cool circuit Richard, using the same transistor
for RF transmit/receive depending on the one PIC pin.
Have you actually got this to work or is it still a
design idea??
-Roman


Richard Prosser wrote:
{Quote hidden}

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2002\06\25@135834 by Lawrence Lile

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Electronic Goldmine ( 1-800-445-0697  )has some IR remote controls and some
reciever boards to match for $5.95 each.  I was wondering if these had a
chance of working in broad daylight.  Has anybody tried IR remotes in
daylight?


--Lawrence

{Original Message removed}

2002\06\25@161743 by hard Prosser

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Roman - I've sort of got half way.

I've got a super-regen working at about 60MHz and it can detect my GDO from
accross the room - using a scope on the output as a detector.
I haven't got as far as connecting it to a micro and writing the software
- let alone making 2 of them & getting them to talk to each other.

Note that the circuit values used in my example are NOT the same as I have
used in my prototype. The demo schematic was only a simulation example.
If anyone's interested I'll update the circuit with real world values,  - I
just can't remember them & haven't got the item here.

Basically I'm trying to come up with a pcb so I can make the receiver
circuit sensitive, reliable & reasonably robust at a useful frequency. Then
the micro stuff & the peripheral stuff will follow.

I have however noted that the receiver will also detect the presence of
nearby micros - which could also be a problem - I'll have to look at my
operating frequency.

I'm gaining enthusiasm however so will get back into it again shortly
Richard P




Very cool circuit Richard, using the same transistor
for RF transmit/receive depending on the one PIC pin.
Have you actually got this to work or is it still a
design idea??
-Roman


Richard Prosser wrote:
>
> OK - Here's the circuit so far - Setup for about 22MHz as the transistor
is
> only a 2N2222
>
> L2 and C4 basically determine the frequency, with some help from C1 & C2.
>
> In RX mode an approx 20kHz pulse train appears at the output with about
> 2.1V to 3.0 V range.  The actual pulse frequency depends on the received
> feild strength in a roughly logrithmic relationship.
> So, the PIC has only to count the number of pulses in a given interval -
or
> measure the time for a number of pulses and it should be able to figure
out
{Quote hidden}

used
> the same basic circuit but with component values altered & a better
> transistor at about 70MHz but have not yet tried making 2 of them &
> connecting to PICs for communication.
>
> One area of possible difficulty is that according to the simulation, the
RX
{Quote hidden}

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2002\06\26@014518 by Peter L. Peres

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On Tue, 25 Jun 2002, Richard Prosser wrote:

...

You could split C2 (2x220p) and use a diode with A at the split point and
K at the pic port, and another from gnd (A on gnd K on split point). This
should increase the separation between tx and rx (superregen) modes but
may quench the oscillator in tx mode if Q1 does not have enough gain.

As you said, there are other ways to do it beyond this level of
complexity.

Peter

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2002\06\26@014540 by Peter L. Peres

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On Wed, 26 Jun 2002, Roman Black wrote:

>Very cool circuit Richard, using the same transistor
>for RF transmit/receive depending on the one PIC pin.
>Have you actually got this to work or is it still a
>design idea??
>-Roman

The cheap children's walkie-talkies you can buy are built like this Roman.

Peter

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