Software Support > Automated Projects
Circuits
DaOld Man:
I didnt want to post this on the Project Announcements section because it is not arcade related.
This section doesnt get used much so I thought it might be a good place to post it.
Project history:
Years ago, I ran a wire (2 actually) out to a microswitch mounted on my mailbox. Open the mailbox door, switch would close.
Inside the house, the closing of the switch would sound a buzzer for a few seconds then turn on a lamp, which latched by a relay and stayed on until you press
the reset button. You got mail!
This was very handy way back then but after a year or two the wire started deteriorating and the circuit began to fail.
Fast forward to about 3 or 4 years ago from now.
I bought one of those wireless drive way alert things at Harbor Freight (around 13 US bucks).
It had a transmitter with a motion detector that you would mount to detect cars coming into your drive way.
When it detected movement, it would send a signal to the receiver. The receiver would make a rather annoying tone and flash three LEDS on the receiver front.
This was great until it rained, snowed, or an insect would set the thing off in the middle of the night.
After a while it got so annoying I just turned off the receiver.
Fast forward to today:
I was bored and weather sucks so i thought I needed something to do.
I noticed the transmitter was still fastened to the telephone pole in my front yard.
I took it off the pole, brought it in the house, took it apart and cleaned out several years of crud (2 spiders did not fare well that day).
Changed out the 9 V transistor battery, dug out the receiver, dusted it off, changed out the C cell batteries, turned it on to my amazement it still worked.
Hmmm, thought I, maybe this has possibilities.
I put the transmitter in my mailbox and tested it. It didnt work. My mailbox is metal so I figured the metal was blocking the signal.
So i brought the transmitter back in the house. I dropped it and broke a chunk out of the Fresnel lens, but it still worked.
I took the transmitter apart and drilled a hole in the back. I then hot glued a plastic PC board standoff in the hole, ran the antenna wire (about a 6" long wire that was coiled up inside the transmitter), through the plastic standoff. I then glued a rare earth magnet holder to the back of the transmitter.
I drilled a hole in the back of the mailbox big enough for the standoff to go through.
Fed the antenna wire and the standoff through the hole and the magnet firmly held the transmitter in an upright position to the inside back of the mailbox.
It worked like a charm!
Open mailbox, annoying sound goes off in house. You got mail.
That was all good but the system was still missing something. I needed a light to latch on in case I missed it when the alarm went off.
So i took the receiver apart and added an scr in the center led. I also added a Normally Closed button mounted to the top to reset the light when I see that I do have mail.
It works real well, and the mailbox shields from false alarms from wind, rain, snow, whatever.
Well pictures are worth a thousand words and since I already have a thousand words, lets continually with pics!
First here is the transmitter, showing the antenna coming out the back and the magnet holder (the magnet stayed stuck to the back of the mailbox when I pulled this out for the pic.)
Here is the transmitter stuck to the inside back of the box:
And the antenna coming through the back of the mailbox:
Here is the receiver board removed from the enclosure. I marked the jumpers that are used to set the channel. The transmitter has the same jumper layout, so you can have more
than one of these pairs just by setting the channel jumpers differently on both transmitter and receiver. They both must match the same pattern:
And here is the rest switch mounted on the receivers enclosure. I got it a little off center but I can live with it.
Another pic of the switch, showing the two wires I soldered to the switch. The white wire is the antenna, I tried to route it the same way as it originally was.
Switch mounted and circuit board put back in place. i ran the switch wires out so i can get to them. Notice the 3 C cell battery compartment.
I then soldered a 330 ohm resistor in one of the wires going to the reset switch, and the other end of the resistor to the POS (+) terminal on the battery compartment.
I then cut the POS side of the LED center wire and soldered an SCR into it. (Will attach schematic in a few).
The gate of the SCR soldered to the wire going into the board (was LED lead).
The cathode of the SCR soldered to the lead going to the LED.
The Anode of the SCR solders to the other wire of the reset switch.
Put enclosure halves back together, installed C cells and tested. Works like a charm!
Here is the receiver, standing by patiently for a new signal from the transmitter.
I walked out to the mailbox and opened the door, came back in and this is what I saw:
It's saying, "hey stupid, you got mail!"
Press of the button turns off the led.
The noise maker and the leds flash when you power this up, so I couldnt use the on.off switch as a rest. Bummer.
And here is the quickly drawn schematic:
I ordered ten of those SCRs from bgmicro.com:
DaOld Man:
I splurged and bought another one of those drive way alert thinggys.
I had a Harbor Freight 20% off coupon and it was burning a hole in my pocket.
After getting home and tearing it apart I was disappointed.
They have changed the circuit boards.
Here is the transmitter with back removed:
Here is the transmitter board removed:
First thing I noticed was it looks cheaper made than the old one I had.
Also, for the antenna it has a coiled spring, not the wire I was expecting.
This wont matter if your mailbox is plastic, but is its metal, the signal wont get through.
I suppose the spring could be de-soldered and a piece of wire soldered back, so the antenna could exit out of the back of the metal mail box, like I did the first time.
But I have no idea if this will mess with the tuning. Maybe some of you guys with radio experience can tell me.
Also, they are using a different chip now, and this one as far as I can tell is not addressable, looks like from info I found on the web, channel is set by capacitors, and they are tiny SMD capacitors,
so changing the channel on these new ones is going to be nearly impossible, however it shouldnt be a problem as long as your neighbor is not using one on the same channel.
The chip in the transmitter is EG0001 if you want to do some research.
Now the bad news.
Here is the receiver with the back removed:
And here the board removed:
The big problem is that these leds are wired with the anodes wired together (positive is common).
That means the chip that turns on the LED outputs a negative to the LED, and not a positive like my first one did.
This is going to make it hard to wire in the SCR like I did before, to latch the LED on.
SCR needs a positive trigger on the gate to fire it.
back to the drawing board I guess.
One thing I do like about this new model, it only has one switch, off/hi/low whereas the other had two, on/off and hi/low.
Thats about all I like about it.
The LEDs still fire for a second on power on so I cant use it to reset the LED. which means I will still need a pushbutton for reset.
DaOld Man:
Well, I wound up the first latch circuit I discussed before getting on this latest trip.
I used an Opto Isolator to latch on the LED.
I had to wire it a little different from my first example, since it had to take a negative pulse to latch on.
Here is a schematic:
A negative pulse from the circuit board fires the opto isolators LED and the receivers LED, through the two 330 ohm resistors, and the on board LED which I have no idea what its value is.
Once the opto isolators LED is on, the transistor conducts, keeping both LEDs on.
This circuit draws at least twice the current that the SCR circuit did, due to both LEDs being on (opto isolator and receiver).
I dont know how this will work when the batteries get weak, the 3 resistors may cut voltage enough to not turn on the opto isolator LED.
But for now it is working.
Here is my Opto Isolator with two resistors soldered to the pins. I am getting the signal trigger off one of the on board LED leads. Im getting the +VCC from the other LED. The + wire (red) goes to the reset button then back to the opto isolator (white wire). The blue wire goes to battery pack, neg terminal.
After testing, I hot glued it to the circuit board to keep everything stable and fastened down.
Got a little sloppy but more is better, right?
I added a piece of heat shrink to cover where the blue ground wire connects to the opto-isolator lead.
And here it is all finished. Board fastened to housing. Reset button mounted and white and red wires soldered to it. Blue wire soldered to the negative terminal on the battery pack.
And that is that. If I use this setup on a metal mail box I will have to come up with a way to get the antenna outside the box.
I may play around with replacing the spring antenna with a piece of wire.
Note to self: the scr method is a lot easier, wish they made a scr that triggers off a negative pulse, but Ive never seen one.
PL1:
--- Quote from: DaOld Man on February 23, 2019, 11:22:30 pm ---Got a little sloppy but more is better, right?
--- End quote ---
As the old saying goes, "The bigger the blob, the better the job!" :laugh2: jk
Scott
DaOld Man:
Then I should be the best LOL.
You know this could be made a lot simpler if I could get into the chip and reprogram it, but I have no idea how they do it, the numbers on most of the chips are rubbed off, so not even sure what they are.
There is no programming port so you would have to do some fancy soldering.
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