Can someone shed some light

L

LBNote

Guest
Hi,

Here is a basic description of the circuit,
PIC16F628
UHF Receiver Module @ ~433Mhz
http://www.computronics.com.au/module/txrxpair/txrx_data.pdf
1 LED
1k Resister
5 Volt regulator, plus 22mf and 100nf caps

I have the PIC simply blinking the LED ~ every 200ms
and the UHF module data output connected to my scope

What I notice is that the UHF data output swings along with the LED, I mean
instead of just showing normal garbage as is the case when no data is being
transmitted.

Problem is NOT present when the LED is removed from the circuit

The module still seems to recover data though.
Can someone give me there thoughts on what's happening, I understand that
something is causing interference,

How can I stop this ?


Lorne...
 
"LBNote" <lbonnell@ozemail.com.ua> wrote in message
news:400499cd$0$893$61c65585@uq-127creek-reader-02.brisbane.pipenetworks.com.au...
Hi,

Here is a basic description of the circuit,
PIC16F628
UHF Receiver Module @ ~433Mhz
http://www.computronics.com.au/module/txrxpair/txrx_data.pdf
1 LED
1k Resister
5 Volt regulator, plus 22mf and 100nf caps

I have the PIC simply blinking the LED ~ every 200ms
and the UHF module data output connected to my scope

What I notice is that the UHF data output swings along with the LED, I
mean
instead of just showing normal garbage as is the case when no data is
being
transmitted.

Problem is NOT present when the LED is removed from the circuit

The module still seems to recover data though.
Can someone give me there thoughts on what's happening, I understand that
something is causing interference,

How can I stop this ?


Lorne...

Do you have good supply bypassing on the PIC? Nice and close to the device?
Click to expand...
Also for the module.

Ken
 
"Ken Taylor" <ken123@xtra.co.nz> wrote in message
news:bu26ge$co94h$1@ID-76636.news.uni-berlin.de...
"LBNote" <lbonnell@ozemail.com.ua> wrote in message

news:400499cd$0$893$61c65585@uq-127creek-reader-02.brisbane.pipenetworks.com.au...
Hi,

Here is a basic description of the circuit,
PIC16F628
UHF Receiver Module @ ~433Mhz
http://www.computronics.com.au/module/txrxpair/txrx_data.pdf
1 LED
1k Resister
5 Volt regulator, plus 22mf and 100nf caps

I have the PIC simply blinking the LED ~ every 200ms
and the UHF module data output connected to my scope

What I notice is that the UHF data output swings along with the LED, I
mean
instead of just showing normal garbage as is the case when no data is
being
transmitted.

Problem is NOT present when the LED is removed from the circuit

The module still seems to recover data though.
Can someone give me there thoughts on what's happening, I understand
that
something is causing interference,

How can I stop this ?


Lorne...

Do you have good supply bypassing on the PIC? Nice and close to the
device?
Also for the module.

Ken


Thanks for your help Ken,
Click to expand...

On the UHF module I have a 2.2uf tant and a 100nf close as I can, but
nothing on the PIC,

Will give that a try tonight, will just the 100nf do or should I use the 2.2
mf tant as well or other values I'm not sure, I don't even know what science
to use to find out the correct values. I just borrowed those values from
another (Similar ) circuit.


Lorne...
 
"LBNote" <lbonnell@ozemail.com.ua> wrote in message
news:4004a197$0$906$61c65585@uq-127creek-reader-02.brisbane.pipenetworks.com.au...
"Ken Taylor" <ken123@xtra.co.nz> wrote in message
news:bu26ge$co94h$1@ID-76636.news.uni-berlin.de...
"LBNote" <lbonnell@ozemail.com.ua> wrote in message


news:400499cd$0$893$61c65585@uq-127creek-reader-02.brisbane.pipenetworks.com.au...
Hi,

Here is a basic description of the circuit,
PIC16F628
UHF Receiver Module @ ~433Mhz
http://www.computronics.com.au/module/txrxpair/txrx_data.pdf
1 LED
1k Resister
5 Volt regulator, plus 22mf and 100nf caps

I have the PIC simply blinking the LED ~ every 200ms
and the UHF module data output connected to my scope

What I notice is that the UHF data output swings along with the LED, I
mean
instead of just showing normal garbage as is the case when no data is
being
transmitted.

Problem is NOT present when the LED is removed from the circuit

The module still seems to recover data though.
Can someone give me there thoughts on what's happening, I understand
that
something is causing interference,

How can I stop this ?


Lorne...

Do you have good supply bypassing on the PIC? Nice and close to the
device?
Also for the module.

Ken


Thanks for your help Ken,

On the UHF module I have a 2.2uf tant and a 100nf close as I can, but
nothing on the PIC,

Will give that a try tonight, will just the 100nf do or should I use the
2.2
mf tant as well or other values I'm not sure, I don't even know what
science
to use to find out the correct values. I just borrowed those values from
another (Similar ) circuit.


Lorne...

It won't hurt anything to put both, particularly as you have UHF floating
Click to expand...
around. The theory basically being that any capacitor will have a series
resonant frequency of its own, so having several in parallel makes it
unlikely that any one will matter. You could even put a 10pF in parallel
with them on the UHF module. I might even be tempted to put a slightly
larger tantalum in on the PIC, maybe 10uF, but it probably won't be critical
as I doubt if it is switching at a high rate internally. If you still have
trouble you could put in an RF choke on the supply to the UHF module.

Cheers.

Ken
 
On Wed, 14 Jan 2004 11:22:20 +1000, "LBNote" <lbonnell@ozemail.com.ua>
wrote:
Hi,

Here is a basic description of the circuit,
PIC16F628
UHF Receiver Module @ ~433Mhz
http://www.computronics.com.au/module/txrxpair/txrx_data.pdf
1 LED
1k Resister
5 Volt regulator, plus 22mf and 100nf caps

I have the PIC simply blinking the LED ~ every 200ms
and the UHF module data output connected to my scope

What I notice is that the UHF data output swings along with the LED, I mean
instead of just showing normal garbage as is the case when no data is being
transmitted.

Problem is NOT present when the LED is removed from the circuit

The module still seems to recover data though.
Can someone give me there thoughts on what's happening, I understand that
something is causing interference,

How can I stop this ?


Lorne...
Click to expand...
Your problem is most likely one of physical construction and wiring.
Your LED will be pulling significant current each time it switches on
(2mA?, 20mA? depends on your dropper resistor). If you supply your UHF
module via the same ground connection as your LED then the resistance
of your ground connection will induce a small voltage drop, enough to
upset your UHF module. The longer your ground connection the greater
the potential problem becomes.

Good practice would be to wire seperate ground connections to your UHF
module and your PIC/LED circuit, from your power supply. This is
called a "star ground" connection. Also you would have seperate bypass
capacitors on each as well (right across the powerpins of each
device). 100nF and 10uF values are common, but their value is not
critical. 22uF (not mf unless you are an oldie!) is fine.

Regards
Dave :)
---------------------------
(remove the "_" from my email address to reply)
 
"David L. Jones" <tronnort_@yahoo.com> wrote in message
news:4004fa1c.596911@News.CIS.DFN.DE...
On Wed, 14 Jan 2004 11:22:20 +1000, "LBNote" <lbonnell@ozemail.com.ua
wrote:

Your problem is most likely one of physical construction and wiring.
Your LED will be pulling significant current each time it switches on
(2mA?, 20mA? depends on your dropper resistor). If you supply your UHF
module via the same ground connection as your LED then the resistance
of your ground connection will induce a small voltage drop, enough to
upset your UHF module. The longer your ground connection the greater
the potential problem becomes.

Good practice would be to wire seperate ground connections to your UHF
module and your PIC/LED circuit, from your power supply. This is
called a "star ground" connection. Also you would have seperate bypass
capacitors on each as well (right across the powerpins of each
device). 100nF and 10uF values are common, but their value is not
critical. 22uF (not mf unless you are an oldie!) is fine.

Regards
Dave :)
---------------------------
(remove the "_" from my email address to reply)
Click to expand...
Yes indeed, I'm with you on this one Dave.

I had a design using the same TX/RX pair.
The receiver would be 'upset' by an RS485 device transmitting.
What a pain that turned out to be... Seems that with all the gain of
the super-regen RX, the slightest power supply ripple would be
seen on the data output. (probably mostly to do with the slicer really)
Decoupling, decoupling and then a bit more decoupling made things
a lot better but still not perfect. The grounding was to a bottom layer
plane in this case and still the noise got through....

The end soloution was to not use the AM stuff.(crap)
Although, someone did mention that applying an offset DC bias to the
analog output (~1Meg -> Vcc) would shift the slicer decision point
to somewhere less sensitive and also stop the noise chatter on the
digital output. I haven't yet tried this but it sounds like a good idea and
would at least give the uart a break... (pun?)

An observation about the TXers. I experienced a bit of difficulty with
the start-up time of the oscillator when operating it from 5 volts. An 8V
regulator was later fitted to supply the TX.

HTHs
Greg the Grog
 
"Grog" <shem_an_na@SPAM_ME_NOThotmail.com> wrote in message
news:WagNb.12416$Wa.2423@news-server.bigpond.net.au...
"David L. Jones" <tronnort_@yahoo.com> wrote in message
news:4004fa1c.596911@News.CIS.DFN.DE...
On Wed, 14 Jan 2004 11:22:20 +1000, "LBNote" <lbonnell@ozemail.com.ua
wrote:

Your problem is most likely one of physical construction and wiring.
Your LED will be pulling significant current each time it switches on
(2mA?, 20mA? depends on your dropper resistor). If you supply your UHF
module via the same ground connection as your LED then the resistance
of your ground connection will induce a small voltage drop, enough to
upset your UHF module. The longer your ground connection the greater
the potential problem becomes.

Good practice would be to wire seperate ground connections to your UHF
module and your PIC/LED circuit, from your power supply. This is
called a "star ground" connection. Also you would have seperate bypass
capacitors on each as well (right across the powerpins of each
device). 100nF and 10uF values are common, but their value is not
critical. 22uF (not mf unless you are an oldie!) is fine.

Regards
Dave :)
---------------------------
(remove the "_" from my email address to reply)

Yes indeed, I'm with you on this one Dave.

I had a design using the same TX/RX pair.
The receiver would be 'upset' by an RS485 device transmitting.
What a pain that turned out to be... Seems that with all the gain of
the super-regen RX, the slightest power supply ripple would be
seen on the data output. (probably mostly to do with the slicer really)
Decoupling, decoupling and then a bit more decoupling made things
a lot better but still not perfect. The grounding was to a bottom layer
plane in this case and still the noise got through....
Click to expand...
RS485 Drivers can deliver/draw quite a bit of current when they Transmit
.........
 
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