433MHz Tx supply voltage

[jodicalhon]

I got all inspired by Stan Swan's "433MHz + Picaxe = Magic" article in the Jan 2006 Silicon Chip, and dashed out to my local Jaycar to buy a Tx/Rx pair.

In about 15 mins after arriving home I was transmitting data from my 08M-based temperature logger to my PC. It was almost embarrassingly easy!

Just a question on the supply voltage for the Tx. The datasheet from Jaycar specifies max 3V supply for the Tx, and 4.5 - 5.5 Volts for the Rx. Stan's article has them both running from 4.5 - 5.5 Volts.

I've been running my Tx from a 78L05 fed by a 9Volt battery with no ill effects, so far. Admittedly, it's only been for in bouts of about 10 mins continuous running.

I only noticed the 3V requirement after seeing some other 433MHz pairs on the net saying 3 - 12V supply and went looking for the data at Jaycar. (I'd done my initial setup straight from Stan's article - noticed your errata, Stan, when I went to get the Basic scripts.)

Has anyone else been running from 5 Volts? Any problems?

 

[Bloody-orc]

i also run mine from 5V but through a resistor. a 270 ohm it is. datasheet sed that i should do that and so i did. and it's forking perfect. only the antenna i have is kinda, well, not so good.

 

[jodicalhon]

Thanks bloody-orc. Mine doesn't mention a resistor.

Altronics.com.au have a different model to those from Jaycar. Their Tx has a specified voltage range of 3 - 12V.

And wouldn't you know it, theirs are on special! Hmmm, I suppose I could do with another pair. Just for comparison, y'understand. (Looks over shoulder to see if the Chancellor of the Exchequer is about....)

 

[manuka]

Another happy customer! Yes- they certainly are easy. The Jaycar Tx, like most, runs 3-12V OK &amp; I run it straight off the Picaxe 4.5V supply. Their Rx however is picky, &amp; stops working ~4.3V. Check =&gt; www.picaxe.orcon.net.nz/433rpt.jpg <A href='http://www.picaxe.orcon.net.nz/433rpt.jpg ' Target=_Blank>External Web Link</a>.

These supplies are consistent with the Tx being in a keyfob whose 12V battery slowly flattens, while the Rx is indoors attached to a mains PSU/7805 etc. Stan

 

[jodicalhon]

Ah, thanks Stan. Nice to know I can up the Tx supply voltage if required.

The Jaycar datasheet (what there is of it), under Absolute Maximum Ratings, just specifies 3V for the Tx. And again states 3v (typ), with no max or min, under Transmitter Characteristics.

The datasheet for the Rx does specify a tighter supply requirement.

Keep those articles coming!

 

[andrewpro]

A curiosity: Has anyone tested signal strength with varying voltages? As in do you get a higher output with 12 volts than with 5v or 3v?

--Andy P

 

[manuka]

Good point - something I shamefully didn't check, although I feel output will remain pretty constant as supply voltage falls. I'd reasoned most Picaxe users would share the normal Picaxe 4.5V supply, &amp; range extensions could be easily achieved with a &quot;Cotanga&quot; Yagi =&gt;www.picaxe.orcon.net.nz/yagi433.jpg <A href='http://www.picaxe.orcon.net.nz/yagi433.jpg ' Target=_Blank>External Web Link</a>