Personally, I think this is getting way over engineered for what should be a simple concept.

I totally agree.
While all the information on transient data is not necessarily wrong, I think it can basically be ignored for this application.
Because we have no way of knowing the design limits of Vcc in the remote transmitter, we must assume that it requires a relatively stable 11.5-12.5 Voltage (the original battery).
The 12V circuit on an automobile varies normally between about 10.6V (starter motor cranking) to about 14.6V (approximate maximum regulated charge voltage. Steady state voltage will usually be 13.8V to 14.2V with engine running and 12.6-12.9V with engine off.
All that is needed here is a DC-DC circuit capable of outputting a constant 12V with a varying input voltage. This can be as simple as a 12V zener with appropriate current limiting resistor to a buck-boost converter that maintains a constant 12V under all conditions..

Personally I would use a 1W 12V zener with a 47 to 56 Ohm resistor (1/2W) in series.
Connect the resistor to the accessory circuit of the car and the cathode of the zener. Connect the anode of the zener to ground.
Connect the + battery terminal of the remote to the cathode of the zener and the - terminal to ground,.

The guiding principle should be the same as the handle of one of the primary contributors to this thread.

Graham

 

But the gate opener doesn't have to work when the car is cranking.

The discharge curve for the A23 battery http://data.energizer.com/PDFs/A23.pdf is pretty rapid with a capacity of 55 mAh to 6V.

The TS, I don't think knows the minimum operating voltage and if that minimum voltage gets the range desired.
Operating the control not near a body part could decrease range too. i.e. A hand pushing a button vs a far away button.

 

All that is needed here is a DC-DC circuit capable of outputting a constant 12V with a varying input voltage. This can be as simple as a 12V zener with appropriate current limiting resistor to a buck-boost converter that maintains a constant 12V under all conditions..

Personally I would use a 1W 12V zener with a 47 to 56 Ohm resistor (1/2W) in series.
Connect the resistor to the accessory circuit of the car and the cathode of the zener. Connect the anode of the zener to ground.
Connect the + battery terminal of the remote to the cathode of the zener and the - terminal to ground,.

Graham

Do you mean do away with capacitor and all that is needed is this?

Thanks.

 

The TS, I don't think knows the minimum operating voltage and if that minimum voltage gets the range desired.
Operating the control not near a body part could decrease range too. i.e. A hand pushing a button vs a far away button.

Not sure if this info is of any relevance:
The external button is about 3 feet from remote. The remote is place near the windscreen. When operating the external button, the remote will not be more than 10 feet from gate. 11.5 V on the variable DC supply will operate the gate at 15 feet. Did not test beyond 15 feet.

 

The TS, I don't think knows the minimum operating voltage and if that minimum voltage gets the range desired.
Operating the control not near a body part could decrease range too. i.e. A hand pushing a button vs a far away button.

Um... The remote was originally a handheld device.

Do you mean do away with capacitor and all that is needed is this?

If it was mine I would still put a good sized capacitor on it but yes what you have there would work to limit the input voltage.

 

Basically, yes but I have to say that I do not like switching the power like that.

Instead of shorting the on board switch I would try to see how it is connected and remote its function.
It probably connects a circuit to ground so it would be easy to bring one wire out from it. If not to ground or VCC than you'll have to bring both wires out.
By switching it as you are, you are powering the uP on and off each time. that's a sure way to bring it to an early death. There is also no assurance that it will behave properly every time... it will not have been designed to expect a closed switch on power and that could affect its initialization.
I agree with tcmtech about adding a capacitor across the zener but would limit it to 220 - 470uF and best to use a 25V or more electrolytic.
Graham

 

How about taping from the original switch instead? Will that now be like operating the original switch?

bummer. just realised that's additional 2 wires (or at least 1 additional wire) going into the remote.

 

Sure. Give it a try!

And while you're at it you might as well wire the LED to trigger and external heads-up display system to project a scrolling message on the windshield saying the gate is opening or closing too.

 

Hmm.... I cannot have any more wire going into the remote. 2 is max.
If there's more than 2 wires, then I would have to hide the remote somewhere like under the dash or something and perhaps compromise on signal strength and hope it will still work. That would also mean I cannot have the heads up display
So, back to finding a good spot for the remote........
Thanks.

 

D2 is in the wrong direction.

D1 is OK to use, but not strictly required. It does offer easy reverse polarity protection.

Could you help me understand how come D2 is in the wrong direction?
If I reverse the direction, does that not result in a short circuit when I push the switch? i.e.
the capacitor will discharge through D2
Or this is a different diode you are referring to?

http://www.eetimes.com/document.asp?doc_id=1279734

 

I cannot speak for @KeepItSImpleStupid but I suspect that he may have been tricked by the fact that you have a red wire on the negative battery terminal. I know it keeps throwing me when I look at your circuits. D2 is oriented correctly and may provide some reverse polarity protection. I say may because the diode will likely fail open and then the remote is still connected in reverse. To avoid this you would also need a fuse that would open before the diode failed.

I am not sure why you are limited to only two wires. If it is a physical thing, your supply leads could be quite small (AWG 20 or 22 would be more than enough for the <50mA loads) The switch wires could probably be even smaller although they soon get so small they are difficult to solder and make physically strong connections.

Graham

 

Could you help me understand how come D2 is in the wrong direction?
If I reverse the direction, does that not result in a short circuit when I push the switch? i.e.
the capacitor will discharge through D2
Or this is a different diode you are referring to?

http://www.eetimes.com/document.asp?doc_id=1279734

NCSailor is correct. D2 is in the correct direction. The RED wire must have threw me even though it was also aware of the +- markings on the PCB.

Sorry.

 

Actually, my bad. Its red because that's all I have!

 

I am not sure why you are limited to only two wires. If it is a physical thing, your supply leads could be quite small (AWG 20 or 22 would be more than enough for the <50mA loads) The switch wires could probably be even smaller although they soon get so small they are difficult to solder and make physically strong connections.

Graham

To be more precise, I should have said that whatever that is going to be mounted near the windscreen has to have 2 wires. Its a very long story so I wouldn't want to bore you kind folks.
For my education, could you kindly show me where the 'antenna' is? I hope its not a pcb trace but a component!

Where is the antenna or the 'thing' that radiates RF.

 

With those types of transmitters simple single piece of wire will work rather well as an antenna although given the largely plastic and composite materials that a vehicle dash is made of the odds are it won't need one anyway. Especially so if you are only needing to transmit a few tens of feet at best.

 

You've learnt something about the perils of swapping out a fairly benign 12-V battery and connecting to the less benign vehicle electrics environment.
With linear regulators at least, there are automotive grade components that are designed to survive the hostilities under the bonnet. I now use these routinely for all the protection they provide. Beware, some versions have low input voltage tolerances such as 6-volt max for a 3.3-volt regulator.
For a simple application like this, I would recommend a 433-MHz transmitter-receiver pair with a three channel encoder-decoder pair like RF Solutions 800E and 800D (I don't work for them, but do use these Keelok chips)

 

With those types of transmitters simple single piece of wire will work rather well as an antenna although given the largely plastic and composite materials that a vehicle dash is made of the odds are it won't need one anyway. Especially so if you are only needing to transmit a few tens of feet at best.

Great! I'll try it out without wire first and if it does not work, then I'll come back to ask where to solder the wire to on the PCB.
Going to try out with 1000uF as its smaller in size than 470uF (not sure why).

 

You've learnt something about the perils of swapping out a fairly benign 12-V battery and connecting to the less benign vehicle electrics environment.
With linear regulators at least, there are automotive grade components that are designed to survive the hostilities under the bonnet. I now use these routinely for all the protection they provide. Beware, some versions have low input voltage tolerances such as 6-volt max for a 3.3-volt regulator.
For a simple application like this, I would recommend a 433-MHz transmitter-receiver pair with a three channel encoder-decoder pair like RF Solutions 800E and 800D (I don't work for them, but do use these Keelok chips)

Yes, and I must thank KISS for helping me to recover the remote.
Hopefully, it won't go puff this time round. It may, just hoping.
To be honest, I don't really understand your recommendation as I know very little. This is beyond me.
Regardless, thanks for your feedback.

 

Your welcome on the remote recovery.

In any event, you can probably take a piece of Coax like RG174 and expose the end (remove the shield only), but try it with no wire first.

 

Yes, and I must thank KISS for helping me to recover the remote.
Hopefully, it won't go puff this time round. It may, just hoping.
To be honest, I don't really understand your recommendation as I know very little. This is beyond me.
Regardless, thanks for your feedback.

Hello
If it got completely messed up, it's easy to put together your own receiver/transmitter pair.
The 800E and D chips do the messy work of encoding and decoding.
Most of these remotes work on the 433-MHz frequency, or 868, or 900 depending on whats legal where you are.
For info, a length of wire 170-mm works well as an antenna for 433, 868 and 900 are shorter - can't remember the exact lengths.
You can make up a shorter antenna by coiling the wire around something like a ball point pen case.
You need to encode as 433 is used everywhere for remotes and you might find a neighbour can open your door accidentally.
If you needed a clean 12-volts, you need a regulator which would have to be a low dropout type.
Personally, I would never run anything other than a light bulb off car electrics without cleaning up a bit.
A 10uF and 0.1uF cap combination are a must across the 12-V, even running on a battery.