Had a problem with a wireless temperature kit.
Bought on Clas Ohlson Art nr.: 36-1795
Type WS590H
The range was very poor and I had a hard time just to pair the transmitter and receiver, even when having them side by side. When paired it usually worked but when the batteries needed replacing it was the same problem again...
After some years I came over this article about increasing range of a wireless BBQ thermometer:
http://www.instructables.com/id/Increasing-the-Range-of-a-Wireless-BBQ-Thermometer/?ALLSTEPS
I investigated antenna lengths etc. and 17cm seem to be the correct length for 433MHz.
The transmitter has a PCB antenna. The receiver has a wire antenna that I measured to 17cm.
So at least this seems it is designed correctly.
I tried to solder a 17cm antenna to the pcb antenna on transmitter, but it did not help much.
Both transmitter and receiver are powered by 2 x AA batteries so 3V when batteries are new, but often a lot less when old.
When reading specs about some 433Mhz transmitters on dx.com I saw that they could
be powered between approx 3V - 12V, and that higher voltage = better range!
I measured voltage on the receiver and transmitter to check if they were powered directly by battery or of they were powered by some higher voltage (perhaps from a dc\dc step up converter\charge pump), but discovered that they were directly battery powered.
I took 2 external 3 x AAA battery cases and powered the transmitter and receiver with 4.5V instead of 3V (actually 2.4V in my case, the bateries were not new), and WOW! Now I could pair them 10M away and receive signal 20M away! I experimentet and found out that the transmitter actually did not need the extra voltage, so the problem seem to be limited to the receiver.
So now the problem is solved?
Yes, but looks a bit ugly with the external battery.
Plan: buy a step up converter to 5V and put it inside.
I ordered on ebay "DC-DC Boost Converter Step Up Module 1-5V to 5V 500mA Power Module New TR"
First I desoldered the LED because I don't want to waiste energy on a LED I can't see.
Then I powered the receiver with 5V.
Problem: the LCD-display went completely black. Seems like it does not like 5V, its a bit too high.
But it's the 433MHz receiver PCB that need higher voltage, so I connected the 5V to the receiver PCB and powered the rest of the thermometer with battery voltage.
And it works.
The only thing I don't know is what effect the transmitter antenna really had, if any. But I did not want to remove it.
Aftermath (have no pictures iof this):
I noticed the LCD display was a tad to dim now. Seem like it (I) got accustomed the the higher voltage.
No problem: I took 2 diodes in series with the 5V and powered the thermometer with 3.8V and now the LCD looks good too.
Pictures of sender, before modification:
I was about to try the antenna-extention method you describe from the Instructables blog. But now I think I'd prefer to try your method to increase the power instead. Can you give me some guidance as to the voltage range for a 915 MHz receiver? I'm not finding my way around the dx.com site well enough to find the information. Any tips you could provide for a 915 MHz device would be appreciated! Thanks!
ReplyDeleteI would just add an extra battery (1.5V) in addition to the batteries the device has today. Mine had 2 batteries (2 x 1.5v = 3V) and 3 x 1.5V = 4.5V hit the sweet spot (as I write, the LCD did not work with higher voltage).
DeleteFor me only the reciever benefited from higher voltage, for your devices it may be different, eg. maybe only transmitter benefit, or maybe both transmitter and reciever. You just have to try:-)
By the way, I'm not concerned about the ugliness factor, so I'm just going to do an external supply.
ReplyDeleteThat makes sense, thanks! I bought two battery boxes and will wire the receiver first to see what happens. If necessary, I'll adapt the transmitter, too. BTW, can you advise how to actually wire the external box (with its red/black wires) to the existing internal battery container? As you can tell, I'm not very experienced with DC wiring...
ReplyDeleteI've tried to find some instructions about wiring the external box to the existing internal battery container, but no luck. Can you advise where to find this info? Thanks!
ReplyDeleteI'm sorry, it is so obvious (to me) I don't know how to decscribe it. The only thing I can say is Red = + = positive and black = - = negative.
ReplyDelete