Touch Activated CCTV Cam 555 ??

[Happy_Jock]

Hi there folks.
I live in a communal block, recently I purchased a cheap door peep hole camera ... http://www.ebay.co.uk/itm/Door-Eye-Spy-Hole-security-Camera-PAL-12V-Power-Supply-/290643081656?pt=UK_CCTV&hash=item43abad79b8

The camera works quite well, however has major disadvantage in the fact I either have to leave it switched on all day long in order to immediately view who is at the door, OR I have to run to the end of the hall turn the plug on then run and back to the tv to have a look.

on seeing a video where a guy constructs this 555 circuit http://www.hobbyprojects.com/quick_circuits_reference/circuits/touch_activated_alarm_system.html

he uses a piezo in place of a relay switch I had been keen to use it as a sort of touch alarm fitting the touch plate on the letter box or handle of the front door, then after putting 2 and 2 together I thought well why not just keep the original circuit design and use it to turn on the peep hole camera when somebody taps the door.

the problem is I am new to relay switches and still in early research of them, im assuming connecting the relay to the main power cable of the peep hole camera would need a "latching" relay ??

as with the schematic not describing any part number or voltage i dont really know what kind of relay to work with ??

any help would be much appreciated.

cheers

[pebe]

Hi H-J. You would need a double pole relay (either a DPDT or a DPST). The contacts of one pole would close to raise the alarm for you. The contacts of the second pole would be wired to C and E of the transistor driving the relay. Then as soon as the coil was energized and closed the relay contacts, the second pole would short out the transistor to keep it latched on. A push-to break pushbutton in series with the second pole contacts would enable you to reset the relay.

[Happy_Jock]

hi pebe,
cheers for the info, just what am looking for, I think I have a few double pole relays in my salvage box,
when u say a push to break button in series with the second pole, could you please tell me a little more on the workings of how this actually resets the relay...(as said im a right newbie to relays)

cheers

[pebe]

Most push-button switches have normally open contacts that close when you press the button. A push-to-open type works the other way round – it has normally closed contacts that open when you push the button.

Using it in the way I suggested, the switch would be in series with the lead from the relay coil to emitter. When the relay was energised, current would flow through the relay, then the second pole contacts on the relay, then through the push button to ground. That would keep the relay energised whether Q1 was switched on or off. Pressing the push-button would break the circuit and the relay would de-energise. This is the same action as the 'Stop' button used on contactors controlling industrial motors.

As you are not using a timed period, then you could simplify the circuit by using the 555 as a switch instead of a timer. I have attached a suitable circuit that uses a standard push-button. It doesn't need a transistor to drive the relay - the 555 can provide 200mA current which is plenty for a relay.

Use a supply suitable for the relay coil you are going to use. Pin 2 is held high by R1. Pin 6 is held low by R2 (it can be any value between 470ohms and 100K). Under these circumstances nothing will happen to Pin3. But if you pull Pin2 low (grounding the door sensor) Pin3 will go high and energise the relay. Pressing the reset button will take Pin6 high, and Pin3 will go low and the relay will de-energise. C1 is to prevent Pin2 being triggered by mains hum picked up on the cable if the unit is some way away from the door - you may need it even if you construct the original circuit.

I hope you find that useful.

[Happy_Jock]

hi agian, this has cleared things up for me a fair bit now, and cheers for this other schematic, it sounds more appropriate for my needs, I am only short of the diode but have ordered some so I can build and test it out on the breadboard. im very keen to begin work using and learning about relays.

incidentally I have already constructed the original circuit substituting the Relay with a piezo to work in the same way but as a type alarm which sounds for a couple of seconds when touched, I ran into trouble with this after copying the schematic perfect, it would not trigger by touching the sensor from pin 2 alone, I found that the only way I could get it to work how the schematic shows was to add a ground wire from the negative rail and attach it to a screw in a light or plug wall plate, or obviously if I touched the touch plate with one hand whiles holding the ground wire with the other. This made some sense I suppose as I have seen other touch plate schematics using 2 leads as the sensors, I was just confused how the schematic I was following did not mention this.

I notice in the new schematic u posted it has 2 arrows going to door, Im assuming the one from the negative rail is again to be earthed???

[pebe]

Hi H_J. Yes, connect the 0V line to earth.

If the timed circuit you built is OK without a cap across the 10M, then if the circuit I gave you doesn't trigger, leave out C1.

BTW, how did you get on with the radio?

[Happy_Jock]

cheers I'll'l be building that by the end of next week, al let you know how it goes.

Yeah as for the Radio, im still gathering the bits and bobs for the more complicated circuit using the hong kong radio, that arrived the other week and as you say its quite amusing the quality for the price. im looking forward to building this as one of my bigger projects when all the components have arrived.

as for the smaller Superregen_2T you suggested, I constructed this and used a mini guitar amp for the output, was pleased in the fact as soon as I powered it I heard music, then whilst adjusting the pot I came across several commercial stations quite clearly, (the first ever radio reviver ive constructed so was quite pleased) I adjusted the small u shaped wire to different sizes but unfortunately didn't seem to come across any air band frequencies, so came to the conclusion maybe im just in an awkward area to receive them with a week receiver. the circuit also had an unusual characteristic in the form of being very sensitive to the point the aerial had to be in a perfectly still position, any time it moved, the speaker made this awful noise which can only be described as a loud "farting" noise lol

[Happy_Jock]

Hi there pebe

just to let you know I have been testing the Schematic you posted and am very impressed with it. However now that i have tested this door flap camera trigger system, i have bumped into a few problems such as the letter flap being non conductive, and having to use the 2 touch wires soldered to 2 thin strips of adhesive copper tape in line along the inner bottom of the letter flap, where fingers will touch both when lifting the flap, it does work but has its problems.

Im rather interested if this relay circuit can work in another way replacing the touch plates with just a switch, or just basically limiting the circuit to activate the relay when the 555 is powered, yet still keeping the reset button in place? my idea now is basically just running some sort of switch at a distance from the relay ciruit which can be pushed in another room to trigger the 555 relay circuit which then switches the camera on....

sorry if iv made that sound more muddled than it is ??

[pebe]

Hi H_J,
Yes, you can fit a push button between the two wires going 'to door sensor' in the circuit. That will connect pin2 to pin1 and turn on the 555.

[Happy_Jock]

Thats brilliant, perfect for my needs, out of curiosity iv gathered that this circuit is consuming power while the relay is on, in this case would it be wise to power it via a dc adapter would you say? or would this cause any unwanted problems?

[pebe]

Provided you have used a 12V relay, then you could use the camera power supply to feed the timer circuit.

[Happy_Jock]

Hi there pebe hope you enjoyed Christmas, finally after all the hassle I can concentrate on this project again, I had been planning to just power the relay circuit separately, but if you say in conjunction with using a 12v relay I could use the camera power supply to power the relay circuit, how would I connect this up and would it effect the operation of the camera when on ??

cheers

[pebe]

Hi H_J, I trust you had a good Xmas - as I did.

I see from your first posting that the power supply for the camera gives 12V at 1A. From its physical size it must be a switch-mode type which gives a stabilized output. So it will happily give the extra power required for your circuit and relay.

Here's how to wire it up. Cut the 12V lead from the power supply and connect the ends like in the drawing. Then the 555 circuit is permanently on, but the camera only comes on when the relay is energised.

[Happy_Jock]

Hi there pebe, sorry it has taken me so long to get back to you on this circuit, just want to say thanx for all your help, it is all installed and working perfectly how I want it to.

much appreciation.