Hi, I have an electric gate opener and want to attach a GSM-activated mechanism so I can "call the gate" to activate it - this means I don't need a button to open the gate.

By shorting terminals 1 & 3 on the control box with a piece of wire, after a small delay, the gate opens or closes.

When I attach the GSM unit to terminals 1 & 3, the gate refuses to move. I have also put a "555 monostable switch kit" in its place - to see if the timing/length of the trigger signal is causing the problem - but this doesn't work either - changing the trigger time does not seem to have the desired effect.

I've made sure the switch kit is normally off (i.e. when provided with the trigger pulse, it then provides a trigger output by shorting the two output wires) - just as if a wire was being placed between the terminals.

Can anybody suggest what to do, or what to measure next to get this gate to trigger with the monostable switch kit - I think this would be the best place to start - then I'll worry about the GSM trigger.

Many thanks,

Charlieboy.

 

Can you post a schematic of the circuit that you put together using the 555?

hgmjr

 

GSM keeps returning Global System for Mobile communications. Your device must be something different.

First of all, you never attach any electronics to a set of terminals that have unknown signals/potentials present. To just hook something up is asking for a puff of smoke to come out ot the device. Always consult the manual, if available, or at least use a meter to see what's there.

If a contact closure was all that was necessary, does your module provide such a feature? That would be a relay doing the closure. A semiconductor device might have been allied with reverse polarity, or the PB made a path for an AC voltage.

 

Here is a link to the PDF of the circuit:

http://tinyurl.com/78ot2q

In terms of "unknown" circuit outputs etc this is a GSM switch which has been manufactured for this purpose, and this is the end desired method of activation. It has a SIM card, and you can phone it. It is a reasonably well established method of closing gates, etc. It recognises the caller_id and activates the circuit based upon a pre-set list of authorised mobile phone numbers.

For now however, I would be happy to get the 555 timer circuit working with the gate - so any advice on that would be very well received - lets ignore the GSM part of the application for now.

Many thanks,

Charlieboy

 

What is the nature of the output signal from the GSM module that is generated when it recognizes the call?

hgmjr

 

It is a completed circuit with a duration of 0.5 seconds. The marketing material says the following "Volt free, momentary relay output, up to 30v 2A".

For now though, I know the gate opens with a wire across the terminals for a period, but cannot understand why the 555 circuit fails to trigger it (I have tested it with a multimeter - resistance drops to close to zero ohms for the set duration)

I believed that if it was a timing issue (i.e. 0.5s) was too short, then I could fix it with the timer circuit (which has an output range from 1s to 15mins). At present, I just have the timer circuit wired up - and it is being manually triggered to provide the output.

Thanks for your replies so far.

Yours,

Charlieboy.

 

I've done a bit more experimentation - the 555 time circuit I've used as detailed in the PDF above DOES work - but the gate seems to be very sensitive to minute adjustments of the pot - and I can't get it adjusted finely enough.

Do any of you guys have suggestions as to how to get a much more finely adjustable pot system to the existing circuit? We're talking down to micro adjustments at the 1s to 3 seconds end of the adjustment scale. (It can go from 1s to 15m).

In case you didn't work it out, I have a very basic understanding of electronics, so your help is very much appreciated.

Thanks,

Charlieboy

 

The output time is determined by the product of C1 and (R1+R2), which is 1000 seconds or roughly 16 minutes, as you know. If you want finer adjustments, say with a center point of 1.5 to 2 seconds, you need to reduce that product. Since you have the variable resistor (pot) already, reduce C1 to 5 uF (approx.), which will give you a max of 5 sec (approx.) and a lot less sensitivity to the pot positon.

John

 

John, Many thanks. I have found a 4.7uF capacitor - so i presume this will give me an upper limit of about 4.7s (there or there abouts).

The question I have is whether the stated voltage matters - I have found ones at 63v, 100v and 450v - Do I assume that this is the upper working voltage of the component? (The current capacitor is rated at 16v).

Many thanks,

Charlieboy.

 

If you are operating at 12V that should be fine. The voltage rating on a capacitor is the maximum allowed. Using a capacitor with a higher maximum is generally acceptable. John

 

John,

Thanks, The 4.7uF capacitor has had the desired effect on the trigger circuit - its much more finely adjustable.

Now to try it on the gate mechanism...

I'll let you know how I get on.

Many thanks for your time. Very much appreciated.

Yours,

Charlieboy

 

I have attached it all up - and it works 95% of the time.

I started to wonder if the terminals on the gate trigger were affecting the 555 timer circuit. I have found out that the gate has a 5v differential between the trigger terminals.

So...

The question now is - what component(s) can I add in-line to stop the 5v differential on the gate trigger affecting my timer circuit?

It seems to be triggering the 555 circuit it on/off during it's swing - because the 5v drops when the gate completes a swing. With my limited knowledge of electronics, I was thinking about a diode of some description - but of course, I still need to allow the trigger terminals to connect for the required period (which I can adjust finely enough now).

Any help, as always, much appreciated.

Yours,

Charlieboy

 

When you refer to the "gate trigger" are you referring to the relay that is being driven by the 555 circuit or the interface between the 555 circuit and the GSM switch? Do you have a way to sketch the circuit you are referring to and show where the 5V potential exists?

John

 

Other questions are where the 555 timer supply comes from? What is its voltage?

Does it changes when the gate is fully opened or closed?

 

John,

Please see the full details here.

Diagram of system

Link to a picture of the installation: click here (This needs to be seen in conjunction with description below).

Problem/Background

I have tried to attach the GSM gate opener to the 555 circuit to ensure the pulse activates the 555 circuit - and it does - so I am still concentrating on getting the 555 timer circuit to work 100% of the time, not just 95% of the time. I seem to have found a timing pulse setting at C which is suitable for both opening and closing the gate.

Because I know the GSM system triggers the 555 circuit OK, I am manually activating the 555 circuit by touching the surface mount trigger switch on the 555 board (same as providing trigger in with continuity at B).

Once B receives a continuity signal, it triggers the relay at C, and should trigger the gate to close at D.

As I said before, I have measured the voltage differential at D, and with the gate not moving, it is 5v. When the gate is moving, it drops to 2v, and goes back to 5v when the action is completed (either completely shut or open).

I think one of the biggest problems I have been having is that the gate mechanism seems to be triggering the 555 circuit once the open or shut cycle is complete - is it possible that the 555 circuit is being triggered by voltage changing between 2v and 5v (see above para) flowing back up to the relay on the board?

Power

The 12v power supply for the for the GSM opener and the 555 timer is directly from the 12v lead-acid backup battery. The gate mechanism is powered from 240v, stepped down to 12v via an internal transformer.

Signal requirements at gate control unit

At the moment, I do not have details of the signal requirements at the gate control, other than it requires terminals 1 and 3 to be shorted. (I have asked the manufacturer, but with no response yet).

Information in each part of the system

For completeness, here are a couple of links to the 555 circuit, the GSM gate opener and the gate opening mechanism.

GSM Gate opener: http://www.aes-ni.co.uk/gsmswitch.php
555 Timer Circuit: http://tinyurl.com/78ot2q (C1 [1000uF capacitor] replaced with 4.7uF cap to give fine control of the pulse time in the region of 1 to 5 seconds)
Gate opening mechanism: click here (9mb in size)


Again, thanks for your help in this matter.

Cheers,

Charlieboy

 

There are several possibilities. Here are some quotes from a Philips Semiconductor application note (attached).

In the FAQ, #'s 5 and 6 may apply:

5. Trying to drive a relay but 555 hangs up. How come?
Answer: Inductive feedback. A clamp diode across the coil
prevents the coil from driving Pin 3 below a negative 0.6V. This
negative voltage is sufficient in some cases to cause the timer to
malfunction. The solution is to drive the relay through a diode,
thus preventing Pin 3 from ever seeing a negative voltage.

6. Double triggering of the TTL loads sometimes occurs. Why?
Answer: Due to the high current capability and fast rise and fall
times of the output, a totem-pole structure different from the TTL
classical structure was used. Near TTL threshold this output
exhibits a crossover distortion which may double trigger logic. A
1000pF capacitor from the output to ground will eliminate any
false triggering.

Also, there is a comment about a prolonged triggerig pulse causing malfunction:

Due to the nature of the trigger circuitry, the timer will trigger on the
negative-going edge of the input pulse. For the device to time-out
properly, it is necessary that the trigger voltage level be returned to
some voltage greater than one third of the supply before the timeout
period. This can be achieved by making either the trigger pulse
sufficiently short or by AC coupling into the trigger. By AC coupling
the trigger (see Figure 3), a short negative-going pulse is achieved
when the trigger signal goes to ground. AC coupling is most
frequently used in conjunction with a switch or a signal that goes to
ground which initiates the timing cycle. Should the trigger be held
low, without AC coupling, for a longer duration than the timing cycle
the output will remain in a high state for the duration of the low
trigger signal, without regard to the threshold comparator state. This
is due to the predominance of Q15 on the base of Q16, controlling
the state of the bistable flip-flop. When the trigger signal then returns
to a high level, the output will fall immediately. Thus, the output
signal will follow the trigger signal in this case.

Inserting a diode from your output to the relay is probably the simplest thing to try (see the appropriate figure in the PDF). FAQ number 6 does not sound like it is the problem you have. So, I would go to the AC coupled trigger. The circuit in the application note requires just a capacitor and a resistor. The capacitor can be almost any value, 0.01 to 0.1 uF would work. One thing to check is when you manually press the switch, do you hold it longer than the pulse length? And, when you use the GSM, does it hold its relay longer than your pulse length?

Finally, are both the gate control and 555 timer running off the same 12V source? For testing purposes, if you substitute another 12V soruce for the 555 does the problem go away?

If I were to wager, I would guess the problem will be solved with the diode. My second choice is the trigger timing.

Good luck. John

Edit: Just noticed you are sinking, rather than sourcing current to the relay. The diode needs to be reversed compared to its orientation in the AN.

 

John,

Sorry for the questions, but a couple of things were not clear to me...

You mention 2 possible solutions (if i read your words correctly)

1) Diode
2) Capacitor and resistor

With reference to 1) (which I read as your preferred option to start), do you mean to

a) put the diode on my output trigger wires to the gate mechanism?

...or

b) do you mean after the 555 pin number 3, after the R2 join, but before the relay in this diagram: http://tinyurl.com/78ot2q (and are you referring to the insertion of the equivalent of D2 in figure 8 as detailed in your attachment in that case?)



With reference to trigger timings, manually, and from the GSM module, they are both shorter than the desired trigger time - good idea though.

With reference to power, they're both running off the same 12v source - the lead acid backup battery to the gate mechanism unit. I do have the option of using a separate power supply temporarily - Do you think using the same power source could be having an effect then?

Thanks,

Charlieboy

 

Sorry for the questions, but a couple of things were not clear to me...

You mention 2 possible solutions (if i read your words correctly)

1) Diode
2) Capacitor and resistor

With reference to 1) (which I read as your preferred option to start), do you mean to

a) put the diode on my output trigger wires to the gate mechanism?
...or

b) do you mean after the 555 pin number 3, after the R2 join, but before the relay in this diagram: http://tinyurl.com/78ot2q (and are you referring to the insertion of the equivalent of D2 in figure 8 as detailed in your attachment in that case?)

I mean option "b", but the diode can go anywhere in that "wire", whichever place is easier. If it is before the junction with R2, the led will be a little dimmer.

With reference to trigger timings, manually, and from the GSM module, they are both shorter than the desired trigger time - good idea though.

With reference to power, they're both running off the same 12v source - the lead acid backup battery to the gate mechanism unit. I do have the option of using a separate power supply temporarily - Do you think using the same power source could be having an effect then?

I have very little experience with garage/gate openers. You found a sag in voltage. It is possible the gate opener is doing the same to the power to the 555, which could affect its operation. I don't think that is likely, because a lead-acid battery is very low resistance and can supply a lot of current. Nevertheless, if nothing else works, it is a variable to consider.

John

 

All,

After much experimentation, I found out that the gate trigger mechanism itself which I was connecting to was unreliable (sometimes worked, sometimes didn't) - so I wired up a spare radio remote control to the GSM trigger system - and now it works faultlessly - so thanks for all you help.

- A bit of lateral thinking I suppose, but it took me 2 months to think of it!

- I did make use of the 555 timer circuit that John helped modify to give finer tuning in terms of trigger timing - so your help is much appreciated.

Cheers,

Charles.