🚀 go-pugleaf

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...

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 :)
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