Simple RF Remote Control circuit Problem - Page 1
Forum section: electronics / beginners

author: zayance
author_rank: Contributor
timestamp: September 20, 2014, 10:27:41 am
content: Hi There,I'm having some problems on a basic Encode/Decode circuit that i want to use as RF Remote.It's based on the famous HT12E and HT12D IC as most people have used for this.I'll be using it with RF Transmitter and Reciever based on Aurel's TX-SAW-MID 3V and RX-MID-3V.But for testing things out i just builded the thing on basic blocks using only one switch and driving only one Led on the Receiver side and a wire from the DATA IN/OUT.And while this one works no prob on breadboard when using same PSU, it doesn't when separating these and having separate PSU's (still using Wire to connect Data IN/OUT, and same adress etc...)And obviously doesn't work neither when using the RF TX/RX modules...All the LED's are just ON, while if i switch to same PSU, the DATA is sent and Decoded properly, and i can control my relay etc...Attached is the Simple Schematic of it all, maybe i'm missing something, but i don't get why i don't have it when all driven with same PSU...Thanks for any clarifications.T.

author: bobcat
author_rank: Regular Contributor
timestamp: September 20, 2014, 11:12:21 am
content: With the direct wire and 2 power supplies, do you have the 2 grounds tied together? On your schematic, the enable pin on the RF receiver is left open. It must be grounded to enable the receiver. You may also have to gate the data in line on the HT12D with the RSSI output on the receiver.

author: zayance
author_rank: Contributor
timestamp: September 20, 2014, 11:25:46 am
content: QuoteNo i don't (works with), so the RF modules take care about this then?QuoteOkQuoteYou mean connect both togetherThanks for your help.T.

author: zayance
author_rank: Contributor
timestamp: September 20, 2014, 11:58:32 am
content: Circuit works, even with the Antennas.The "Common" wiring got me confused, as i wanted to use it as RF etc....Now i'm using breadboard, and RF signal is a little wiggly since it's not a properGND plane etc....But i'll be using these as antenna's, is it ok you think? Datasheet says a Whip Antenna of 16.5mm 1mm thickness copper should do, butwhat about this? Just wondering:http://www.farnell.com/datasheets/605458.pdfThanks again.T.

author: bobcat
author_rank: Regular Contributor
timestamp: September 20, 2014, 01:29:51 pm
content: QuoteI meant gating via an AND type circuit. But if it works without, dont bother.The rule of thumb that I use for minimum ground plane size is the square mm of the plane should at least equal 1/4 of the wavelength used. So, for 434 MHz at 693 mm wavelength, the minimum ground plane should be 693/4=173.25mm2

author: zayance
author_rank: Contributor
timestamp: September 20, 2014, 02:28:29 pm
content: hmmm, well not sure if my PCB design is optimum then.Wanted to etch some boards going like this, but the board itself is small because it willbe places in a small box so... and Single sided, wich doesn't help neither but might give it a shot.What do you think?Thanks a lot for your help.Screen capture of it. and Schematic attached.EDIT: I've done double sided before on my little etching lab, might just add a copper GND plane on top as welland go for that? Maybe add Vias to help as well.What do you suggest?

author: bobcat
author_rank: Regular Contributor
timestamp: September 20, 2014, 03:58:08 pm
content: Don't connect the RSSI output directly to the data output on the receiver. That will damage the module.Sometimes it's not possible to do an optimal PC board layout, especially when trying to reduce size. It will work, but the range will not be optimal. Also the symmetry of the ground plane around the antenna can affect the radiation pattern, making it somewhat directional.If you add a ground plane on the top side, check if that will affect the impedance matching of the trace to the antenna.With constraints such as size, just do your best.

author: zayance
author_rank: Contributor
timestamp: September 20, 2014, 07:39:33 pm
content: I just updated the Layout a little (i can still optimize a little i think), but i guess the Antenna connection might be "cleaner" this way, and from Datasheet seems like adding a a GND plane on the opposite side is recommended for the 50R line, so i'll see if i'll bother on doing a GND plane with Vias made of resistor leg or not (every 15mm from datasheet) but I'll give this one a go for etching and test drive.What do you think? A little better i think no?Since i want to place the antenna inside an ABS box, again size and Real estate limits options unfortunatly.So basically if the Little 434Mhz Antenna with SMA Connector works ok with this circuit, then cool.Thanks again for your help, much appreciated.T.

author: bobcat
author_rank: Regular Contributor
timestamp: September 20, 2014, 08:24:06 pm
content: Yes, much better layout. Making the transmission lines shorter and more direct helps a lot. And you have much more ground plane around the antenna.If you decide to spin a 2 layer board in the future, I suggest putting the transmission line on the top layer and flood the bottom layer ground plane where the transmission line is currently placed.Let us know how well it works!

author: zayance
author_rank: Contributor
timestamp: September 21, 2014, 10:29:17 pm
content: At the end i used a Veroboard for this one, and simple copper wire as antenna, seem to be working ok.Before starting to Etch, i saw that my Dremel was actually no good no more duh, i used it for other stuff, andit wears the thing easily, drilling with cardbide would have been a mess, the axing is trembling too much now...Anyway, 20 to 30m distance with walls and all didn't cause any trouble, who would have tought.You live you learn.Thanks again for your help.T.

author: bobcat
author_rank: Regular Contributor
timestamp: September 22, 2014, 01:20:59 am
content: Good to hear that it is working well.Happy to help...