Semefab - Page 1
Forum section: electronics / general

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 01:31:57 am
content: I have a Stanley 1050 garage door remote opener that has been acting up(the 9V battery reads EXACTLY 9V(from my Extech EX330 meter) so its not that) so i am interested in seeing about doing a bit of reverse engineering of this, its mostly just a 10 postions DIP switch, and some resistors, caps and a transistor, switch, and LED. The only other part(that must do most of the work) is a ship labled:SEMEFAB051-87289515-DAlso has a big "D" on the right hand side(the same size as all 3 of the lines above)I am guessing the last line is the Date of Manufacture(the date on the board is 09-95(yes 1995)I have replaced the LED(as the old one was all bent up) and the tact switch, as i thought maybe the old one was bad(and after i replaced it lasted for a little bit(2 months mabey) until now, i used it probaly 2-4 times a day) Yet my parents openers(from the same vintage) have little to no issues electronics wise(they plastic "push button" has broken, but thats not what i care about, lol).I'll try and take some pics of the board later, but for now does anyone have any ideas?

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 01:59:23 am
content: PICSand yes i know up by the LED/Diode the soldering is messed up, that was me, i lifted a Pad/Trace that connected the LED to the Diode, so i hacked them back together with solder, but the LED lights up when i press the button, and If I go out or back door(that leads to the garage) i can get the remote to work. It will work sometimes in my car, but lately not so much, i also tested the battery voltage "under-load", i pressed and held the button down and got a voltage(off of the battery) of 8.92 Volts(with the battery connected, but no buttons pushed i get 8.97 Volts). and the same battery disconnected i get 8.99 Volts. If anyone wants me to get any voltage measures anywhere else on the board, or continuity, resitance ect(basically anything the EX330 can measure) i can get those. I don't have a scope so i can't really get any look at that stuff.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 04, 2011, 02:11:06 am
content: The transmitter probably drifted. The blue capacitor adjusts the frequency. Mark its initial position, then use a plastic screwdriver to adjust it for more range.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 02:15:36 am
content: Thats what that blue thing is?both of the leads connect to the same trace

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 04, 2011, 02:27:54 am
content: Quote from: mitpatterson on January 04, 2011, 02:15:36 amThe PCB trace is an inductor. At RF, a piece of wire cannot be assumed to be a short circuit.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 02:30:59 am
content: ah ok, i'm not an "EE" by any means, let along know much at all about RF, lol, so basically that is what they are using for a antenna?(the area around that "trim cap")Now if i where to redesign this, how could i add an external antenna(for increased range) even if just a piece of wire in the case, or would that not work?

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 04, 2011, 04:36:02 am
content: http://www.talkingelectronics.com/projects/27MHz%20Transmitters/27MHzLinks-3.htmlhttp://www.talkingelectronics.com/projects/WirelessDoorbell/WirelessDoorbell.html

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 04, 2011, 10:41:21 am
content: i'm thinking to post a thread asking similar thing (rf circuit) but using sometype of rf transistor inside. but later, for now, i'll be watching this thread with interest, i'm looking on how the basic thing to create a 400++MHz RF circuit and how to increase the range (without power boosting amplifier will be more interesting). @mit: any chance dismantling the receiver and show the circuit? you are showing the transmitter right? i cannot connect to nihao's links.. is it just me?

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 03:43:09 pm
content: Quote from: shafri on January 04, 2011, 10:41:21 amThe links worked fine for me, but probably can't dismantle the receiver, as i'm sure its part of the actual opener and my 'rents might not be too happy about that one(especially if the opener stops working)

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 03:52:20 pm
content: Also, here is the schematic the best i could do of reverse engineering it(by tracking the traces) please note there are 2 resistors(i assume) that are missing on the actual board(always been like that) that are not noted in my schematic. I have also laid out the board in eagle trying to keep the size(i measured the traces with my calipers) and shape of the traces as close as possible as not to mess with the RF part, granted the layout/routing as is might not work, not sure how much tolerance there is with the tracks. But here they are as images, the schematic and board. if anyone wants the original eagle board and schematic files let me knowAnd the values i used are what i could get based on the color codes on the resistors and numbers on the caps, couldn't find any numbers on the "trimmer cap" so i just put the value as "trimmer cap"

author: Zero999
author_rank: Super Contributor
timestamp: January 04, 2011, 06:42:39 pm
content: I think the green thing which looks like a 1 Ohm resistor is an inductor.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 07:29:42 pm
content: Quote from: Hero999 on January 04, 2011, 06:42:39 pmFunny thing, I was talking a friend that i know online who does a service similar to Batch PCB(pcb.laen.org) and pointed him here and he said the same thing, lol. He said that based on the color it would be a 1uH inductor, he said it was part of the antenna(or what ever)

author: Zero999
author_rank: Super Contributor
timestamp: January 04, 2011, 07:53:05 pm
content: 1µH makes sense and it's probably a choke rather than part of the tank circuit.

author: mitpatterson
author_rank: Regular Contributor
timestamp: January 04, 2011, 07:56:20 pm
content: Quote from: Hero999 on January 04, 2011, 07:53:05 pmWay above my head, lol

author: Zero999
author_rank: Super Contributor
timestamp: January 04, 2011, 09:18:47 pm
content: Inductors have a high impedance to high frequencies and a low impedance to low frequencies. An inductor used to block high frequencies is often called a choke. Some oscillators use a radio frequency choke to prevent RF from being leaked away up the power supply.

author: no.1134
author_rank: Newbie
timestamp: September 15, 2016, 04:28:39 pm
content: I found a circuit. Long story short, I cannot find the datasheet for an IC labeled:SEMEFAB051-87281231-D(LF)It also has a "D" shaped symbol on the right hand side of the label.Have you by any chance possibly aquired its datasheet?Or is there any way to request it somehow?