Advice please Hippy.

[BrendanP]

Some time ago you told me about using a 0M8 as a 'front end' picaxe for RF reception. The 0M8 monitors the incomming RF signals and when one arrives with the correct header info the 0M8 passes it through to the 40X1. This prevents the 40X1 continually stopping to check all the spurious Rf signals floating around. (I'm mentioning this in case some of the newer members read the thread so they can understand the problem).

At the time I bread boarded the design and it worked fine. I had a look at the layout on that breadboard and have reproduced it on another except with a 151.300meg RF unit rather than the 433meg I used before.

I am also running the picaxes on 3V rather than 4.5V as before.

First question is what value should the R be that is put accross pins 4 and 1? I used a 38K previously, I dont think that was what you specifcially advised, it was what I had to hand and it worked OK. It wont work with the current set up however. Perhaps this is because of the change in voltage Im running the picaxes off.

Is there a formula to calculate the R value needed or is hit and miss?

I have pasted the program below.

main:
low 4 'Rf data comes in on pin 4
serin 1,n2400,("2006"),b1 '2006 tells the reciever that its from one of its transmitters
if b1=88 then alpha 'b1 value tells the 0M8 what function to do
goto main


alpha:
input 4 'set 4 as a input so it passes data through 0M8 to 40X1
low 2 'turn on the led 'LED on shows valid data received
pause 500
high 2 'LED off
goto main

When I use the 'low 4' and 'input 4' parts of the program it doesnt work at all, ie. the LED dosen't light. If I delete those parts of the program it works fine but the 40X1 serially triggers on every RF signal what ever the byte value or header used.

Any pointers?

 

[hippy]

Is that resistor between pins 4 and 1 in the serial line from one PICAXE to another ? If so anything from 200R upwards should work. Or perhaps it's using pin 1 to clamp the pin 4 line to 0V to stop the serial getting to the 40X1 ? In which case I'm not entirely sure what it would need to be.

It's been a long time I'm afraid and I cannot remember the details ... do you have a link to a circuit or earlier post to refresh my memory ?

 

[BrendanP]

I'll dig through my notes and get back to you. I printed out your post at the time. My notes got a bit disorganised with our recent change of address but I should be able to find it.

 

[eclectic]

http://www.picaxeforum.co.uk/showthread.php?t=7064

?
e.

 

[hippy]

Thanks eclectic, that seems to be the one. I edited my original post and the ASCII Art is now readable again

The 47K isn't critical, it just has to be large enough to not damage the RF output when the 08M puts its output low. R=V/I, where V is RF's supply, I is whatever sourcing current the RF can handle. At 3V, if the RF can source 10mA that's 300R upwards.

 

[BrendanP]

Thanks eclectic, I should of used the forum search before asking Hippy again. I didnt know if the term 'front end picaxe' was something I had made up in my mind or was what it was called....
Thanks Hippy, I just got home from work I'll try it again.

 

[hippy]

I tend to call anything which sits in-front of something else a 'front-end'. In this case I suppose it's perhaps technically incorrect because a front-end is usually something which data would pass through before its final destination whereas this works alongside the data stream.