Key FOB Remote more info - 315Mhz vs 433Mhz

Ron Czapala · 2013-05-20 14:49

Parallax Key Fob remote

I suppose I could experiment with this but decided someone might know the answer immediately,
for maximum range, should the coiled antenna be uncoiled or left coiled?

I did determine the VT pin goes high when any of the buttons is pushed.
I wonder how many milliamps the outputs can handle - I suppose using a transistor or ULN2803a would be the safest approach.
Maybe the small IC is a ULN2803...

EDIT: Opps! Forgot that ULN2803 can only SINK current

localroger · 2013-05-20 15:26

Uncoiled. The antenna wire should be 17.3cm long for 1/4 wave at 433 MHz.

Ron Czapala · 2013-05-20 15:35

localroger wrote: »

Uncoiled. The antenna wire should be 17.3cm long for 1/4 wave at 433 MHz.

Thanks! The actual uncoiled length is 10" (25.4 cm).

Should I trim it to 17.3 cm?

What is the formula? I found this one: Length (feet) = 234 / Frequency (MHz)
That would be about 16.5cm.

Ron Czapala · 2013-05-20 18:01

Found some more information on the receiver and ways to set it for Latch, Momentary or Toggle modes with jumpers
Output
A.singnal inter-locking (Latch ) ----connect 2 & 3 ;
B.singnal non-locking (Momentary) ---- all disconnect ;
C.singnal self-locking (Toggle) ---- connect 1 and 2 ;

localroger · 2013-05-20 19:25

Ron, that formula you found is an approximation. In a situation like this, where you're not working with a ground plane anyway, it's good enough. These small antennas can be very weird depending on what else is around that conducts electricity. In general, 1/4 or 3/4 wave is better. Light travesl 300,000,000 meters/second, so at 433 MHz one wavelength is 69 cm and 1/4 wave, generally a good antenna length, is 17.3 cm. For best range it should be sticking up vertically from a nice ground plane.

wass · 2013-05-21 01:57

localroger wrote: »

generally a good antenna length, is 17.3 cm. For best range it should be sticking up vertically from a nice ground plane.

True for a transmitter, but in this case it's just a receiver and subject to a lot of noise. I've done a bunch of experimentation with 433MHz superhet receivers and have found that an "L" shape wire gives the best results in general for reception in all directions (not necessarily in a plane). Additionally I've found that random lengths between 1/4 and 1/2 wavelength work well.. The 25.4cm wire that this receiver came with might be fine if you bend it into an "L" shape.

Ron Czapala · 2013-05-21 10:19

FYI

I soldered a tiny switch between solder points 1 & 2 (see image in post #4) and now the pushing the key fob buttons toggles the outputs on and off.

Ron Czapala · 2013-05-22 08:33

localroger wrote: »

Uncoiled. The antenna wire should be 17.3cm long for 1/4 wave at 433 MHz.

I think I discovered why the antenna is approx 24 cm. The crystals SAW resonator/filter on the key fob and receiver are "HR315" and "BX R316.8" respectively.

Seems these are 315MHz versions - not 433MHz.

The docs on the Canton-Electronics.com site say the antenna length on the 433MHz receiver is 18cm and 24cm for the 315MHz version

Clock Loop · 2013-05-26 16:36

The larger IC looks to be a RX3310a
http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/keyfob/List/0/SortField/4/ProductID/904/Default.aspx
700-10016-L.jpg

I am guessing the secondary smaller chip is a uln2003 or similar driver IC. each of the outputs allows 40ma @ 5v. After I purchase another key fob, and hope it works this time, I will scope it out to determine second smaller IC type, and then repair it.

More images of possible chips... I ordered one of these and it arrived bad, the little IC gets too hot to touch, and because they purposefully erased the ic type, I cannot try to repair it.. I am forced to rma it and waste all that cost in shipping...
shipping alone will cost more than device with rma.

erasing the ic info is evil, pure evil. dosen't allow the ee's to recycle.
And it pisses them off so much, they WILL completely reverse engineer it, and then purposely compete, for the principal. (and they won't even need to erase the ic info)

http://www.spiriton.com.tw/download/ic/RX3310A_1.pdf

http://en.cj36.com/cp/html/?285.html

Clock Loop · 2013-05-26 18:03

The smaller chip is as such.
I think its a pic chip. It decodes the data from the rx chip and outputs the lines. You can see this if you probe pin 13 of the smaller ic while pressing one of the remote buttons

. I also think the pic chip has its data input pin with internal pullup/down. The data looks sharky when free floating.
And datasheet on dataout from the bigger chip, rx3310a, shows pull resistor.
This smaller chip also accepts input from big button, and outputs indicator led state.

Pins 4-7 are probably jumper inputs/programming.
40ma 5v seems dooable with pic chip.
Top view
Dot in upper left chip.
Pin

Left side                               Right side
1-vcc (5v)                               14-Gnd
2-resistor to switch                     13-Serial data from rx3310a
3-Indicator led                          12-VT
4-?                                      11-D4  
5-?                                      10-D3
6-?                                      9-D2
7-?                                      8-D1

This whole design can be redone with the propeller, or stamp,etc.. the RX chip's accepted operating range is anywhere between 3v-6v.
Now you know why the faces were rubbed off. Easy bypass of all other parts direct desired microcontroller interface to rx3310a, in all applications.

I would have never even cared and stopped, when I saw the chip was a pic with a program, I wouldn't have tried to find out what chip the bigger one was, or even looked at it much.
But when I saw they were intentionally rubbed off..... well now... someone wants to play.

First to make pcb with rx3310a type chip interfaceable to stamp/prop 5v/3.3v with program, wins mad props? lolz
(hmm me thinks that whole rubbed off face thing didn't quite work out so well)

One could always skip all this round about Smile with the rx3310a chip, and go to a different chip via digikey...

Enter the $2.40
Si4320 Universal ISM
Band FSK Receiver

https://www.silabs.com/Support Documents/TechnicalDocs/Si4320.pdf

http://www.digikey.com/product-detail/en/SI4320-J1-FT/336-1627-5-ND/2022307

This ic manufacturer has other rx/tx chips also...
http://www.digikey.com/product-search/en?FV=ffec619c

Clock Loop · 2013-05-26 18:47

That was fun, thanks foreigner attempt at obscuring a chips part numbers... I found a great tx/rx single chip solution manufacturer, affordable too.

http://www.silabs.com/products/wireless/pages/default.aspx

http://www.digikey.com/product-highlights/us/en/silicon-laboratories-ezradio/2151

Clock Loop · 2013-05-26 18:57

Here, have a nasaly, ez radio, product introduction.
http://dkc1.digikey.com/us/en/tod/Silicon_Labs/EZradio/EZradio.html

Chris Savage · 2013-05-28 15:33

Clock Loop wrote: »

Thanks parallax, and a foreigners attempt at obscuring a chips part numbers.

I assure you, no attempt was made by Parallax to obscure any part information on 3rd party products. If they are obscured, that is how we get them. This particular product is a convenience item we carry. We do not manufacture it.

Clock Loop · 2013-05-29 15:24

Chris Savage wrote: »

I assure you, no attempt was made by Parallax to obscure any part information on 3rd party products. If they are obscured, that is how we get them. This particular product is a convenience item we carry. We do not manufacture it.

Oh, yea, i didn't mean it like that. I just meant thanks to parallax for providing affordable product, doing all the effort testing them and even offering stuff that might be questionable....
The thanks to the foreign people for obscuring the chip, was sarcastic. I should have split that sentence.
I am familiar with doing business in foreign markets, and know that they think obscuring something actually works for some use, when really it just wastes time invested paying someone to do it.

If parallax wanted to make something similar, im sure they'd just use the $3 easyradio, 3-5v version on a breakout pcb.
I ordered another key fob so i could have a working receiver with two remotes.

Sorry for the confusion.

Ron Czapala · 2013-05-30 12:22

Hurry, Hurry - only 8 Key Fob units left!

I wonder if Parallax plans to keep offering these???

Steph Lindsay · 2013-05-30 12:46

Ron Czapala wrote: »

Hurry, Hurry - only 8 Key Fob units left!

I wonder if Parallax plans to keep offering these???

Yes, we just ordered some more.

LoopyByteloose · 2013-05-30 12:57

I have one of these purchased locally in Taiwan many many years ago. They are a popular item and easily available.

But I am surprised that the Parallax item can be modified to toggle the outputs. That can come in handy.

Clock Loop · 2013-06-03 15:57

My receiver unit arrived today, and I was able to get it working with two remotes. Very easy, push the button, press the remote button.. Now the receiver accepts both remotes commands.
Fun stuff!

Tim-M · 2013-06-03 16:21

Hey Loopy,

Take a look at Post #4, this unit can easily be set to toggle the outputs...

Tim

Clock Loop · 2013-06-03 17:29

I use a spare RE030006 pcb relay with this, it works great.
http://www.digikey.co.uk/product-detail/en/1393217-2/PB742-ND/813808

Key FOB Remote more info - 315Mhz vs 433Mhz

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