MAKE: Electronics: Experiment 15 (Burglar Alarm)

EXPERIMENT 15: INTRUSION ALARM (REVISITED):

(this video is showing how the relay is wired up, once the sensor circuit is broken (open) the relay energises, when the sensor circuit is closed, the relay stays energised)

Part 1: Stripboard Layout:

This experiment calls for a protoboard in the same layout of a breadboard, which does seem a great way to introduce beginners to transferring projects from solderless breadboard to permanent perfboard. However I found this nigh on impossible to find in the UK. I settled using a perfboard and arranging the layout in a somewhat similar manner to a breadboard.

The picture shows the top side and under side of the board, I have mirrored the photograph so the top right of the up side = the top right of the under side, basically, you can overlay the pictures over each other as they correspond (I'm not really sure how to say this more clearly!)

From MAKE Electronics: Experiment 15: Burglar Alarm

At the top of the board is the alarm circuit created back in experiment 11. At the bottom is a circuit that when triggered by an opening in the sensor circuit (i.e. opening a door) turns power on to the alarm circuit. If the sensor circuit is then closed again (door closed) power is still supplied to the alarm so it does not turn off. This is explained exceptionally well in the book however I think I only truly appreciated how the circuit worked when making my own (far less elegant) arrangement on a breadboard to see how it all worked from the schematic diagram.

I soldered everything on the stripboard first, then I took a dremel to it with a cutting wheel and trimmed it down and then sanded the sides, it fits in just between the slots in the project box so I don't have to screw it down (very convenient!).

Part 2: Project Box

The point of this experiment is to show how one goes from a fairly minimalist circuit on the breadboard to a fully-fledged project. This requires casing to maintain the longevity of the project and also somewhere to mount a user interface. The UI for this project is fairly simple, it consists of:

(i) An Arming button - arms the alarm (and lights green LED to indicate the alarm is armed)

(ii) A Test button - (un-armed) lights up LED when sensor circuit is close, (armed) tests alarm circuit/speaker

From MAKE Electronics: Experiment 15: Burglar Alarm

I added some banana plugs to my magnetic sensor, I currently don't have anywhere to put it, Platt says later in the book that I'll learn how to integrate an 'away from home' feature and add a keypad to it (Hopefully I can figure out how to use a matrix keypad instead of a common pin type keypad) So I might get round to using it pending on how well it turns out. When activated the alarm isn't exactly loud so I will build an amplifier circuit at some point (I tried driving it with an old amp and it goes fairly loud for its size, it can certainly be ear piercing)

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Get your own

ATX Bench-top Power Supply

I made this on the weekend. It's a converted ATX PSU, I cut the cables off and added binding posts to use as a bench-top power supply, I could have simply bought one of those cheap ones on ebay from china for ~£40 however I had this lying about and it cost me about £6 in parts.

First I took apart the PSU and took the PCB out after marking the top heights of the components on the case so I could figure out how to arrange the binding posts & fuses. I then drilled and sanded the holes (time to buy a hand reamer).

The wires colours correspond to the voltages:

Yellow - 12V

Yellow/Black - -12V

Orange - 3.3V

Red - 5V

Black - ground

I desoldered a bunch of these which I didn't need clogging up the case, and then cut the others down to a reasonable length and heat-shrinked them (so far no shorts). I then soldered the leads corresponding to the voltages I wanted; 3.3V, 5V, 12V and ground to their corresponding fuse holders and then from the fuse holder I soldered wire with crimped connectors on the end (to be used with the binding posts), hooked them up and voila, all I had left to do was to attach a switch from ground to the thin green wire which turns the power supply on and off when it is plugged in.

I mounted the fan the other way around as the binding post obstructed it from being in it's original position, I also put the fan guard on underneath as I didn't want the fan and the wires to hit each other. I used 5A quick blow fuses as these things can output ~20A and I'd rather not see my projects go up in flames if I can help it.

If you're looking for a 'how-to' vs. an 'account' I suggest looking at these links, which I used when making this power supply, I see no need to saturate the web with another set of instructions!

http://letsmakerobots.com/node/1355 (I'd like to note I do not use a load resistor, I didn't buy one and the supply seems to function ok without it)

http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/

http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/

One final note, if you do undertake this project, be very careful of the power caps inside, I left my supply off for a week before touching it, I'd rather be on the safe side!