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Electronic timers

— Posted by balor on 4:56 pm on Jan. 15, 2002

Im looking for electronic timers with a digital time remaining screen.Ive looked at a lot of electronic suppliers to see if they sell anything readymade.The best that Ive come up with are analogue relay timers 12 and 24v with a twist face to set the delay but patching together batteries to get 12 or 24 volts is not desirable as it takes up precious space.Something with a 9v input and 9v or slightly less would be acceptable.Any info on kits or circuit diagrams would be brilliant even if they do not have a screen.I am not interested in anything thats expensive to build.

— Posted by dellexo on 2:24 pm on Jan. 17, 2002

Iv’e read (not tried) that quite a few timebombs used timers from a normal V.C.R.These can often be set for up to a year.Don’t no what voltage these work at but i would of thought about 6-12 volts.

— Posted by balor on 3:46 pm on Jan. 17, 2002

I know about that Dellexo but I couldnt exactly justify stripping one VCR for the sake of one timer since Im after a low cost timer.I could find no right kits for sale as they could easily be used as bomb timers in the spec that I am looking for.

— Posted by dellexo on 3:54 pm on Jan. 17, 2002

Just a hunch but you could try a plug in electronic timer(the type used to switch on/off household appliances).Most of these have a battery backup which opperate a relay.might be worth a go,nice and cheap too.

— Posted by dellexo on 4:11 pm on Jan. 17, 2002

how about a battery opperated travel alarm clock?.Don’t know what voltage they opperate on but it’s enough to power the speaker quite loud.You could use a small relay in line with the speaker output linked to a 9v battery.Should work O.K.

(Edited by dellexo at 4:14 pm on Jan. 17, 2002)

— Posted by balor on 3:56 pm on Jan. 18, 2002

I thought about the plug in timers but I think that with most of the brands on the market the battery backup only operates the clock and not the relay contacts as the coil is usually mains voltage rated.Probably the travel alarm clock is the best bet but I have been thinking of a relay rated for 12v.Putting a large capacitor in series with the coil and wiring the output off the normally closed contacts so that when current is flowing in the coil as the capacitor is charging the N.O. contacts are open and upon the capacitor being charged the contacts close making the secondary circuit.But if I was using a relay at all I might as well use the battery run down method in which when the battery runs out of energy the N.O. contacts close making a separately wired and powered circuit.These arent easily adjusted circuits and so not very desirable but they might have to do.For some with real electronic knowledge timers should be fairly basic projects but it is very hard to get relevent info on the subject.Everybody knows about using fuses as a delay in explosives and they talk about electrical blasting caps but nobody seems to have an easy and versatile delay method to fire these electrical blasting caps.They all seem to use the dried bean,clothes peg and solder or egg timer with metal fillings which arent always very appropriate.It would be so much easier to have a timer in which you type in or set the delay and it works exactly everytime regardless of interference or atmospheric or outdoor conditions.

— Posted by dellexo on 6:55 pm on Jan. 18, 2002

Yea’h,know what you mean about the battery only keeping the clock going and not opperating the contactors(relay)it was Just a idea:sad:Checked on the net and you can bye timers that opperate on 12v.d.c. and having a switching of 240v a.c. 6A cost about 20.

— Posted by Sicopath on 4:14 am on Jan. 19, 2002

VCR parts are in easy supply, I used to live close to a TV/Video repair place and they had piles of surplus junk out the back. As I was only 12 or so at the time, I usually just stole little electric motors and LED’s

— Posted by balor on 1:04 pm on Jan. 19, 2002

I checked on a search engine again and found a lot of shit but after a bit of searching.All of what I found before were countdown timers with no output.I found a couple of sites that sell something suitable.Most if not all are kits and sell for about $17 to $25.If you want to check them out   http://www.electronickits.com
Check out the timers rated 12v as they will also work with 9v(handy battery assembly), The ones mentioning a relay output.There is a bit of other shit for sale as well such as counters and countdown timers that have no output so are useless so just to be aware of that.

— Posted by Hergor on 7:11 am on Jan. 23, 2002

this travel alarm clock sounds good to me. but you don’t have to use relays to trigger the ignition circuit.
how about transistors?

lets say the alarm clock runs on 3 AA batteries which adds up to 4.5 V. i suppose the alarm-speaker uses at least 3 V. this is much more than what you need. (basically the cheapest transistors switch at about 0.7 V)
and if you use thyristors the secondary circuit (the trigger circuit) will remain closed after even if the trigger impulse is very short (usually the impulse emitted by the primary circuit is too short to ignite the electric ‘fuse’ – those triggers used for model-rocket engines)

if you need any plans i can give some to you…

— Posted by balor on 5:19 pm on Jan. 23, 2002

Thanks Hergor!I never thought of Thyristors.Seem the way to go as regards a battery alarm clock as the secondary will remain supplied regardless of the duration of the trigger pulse.Would solve a lot of problems!

— Posted by ActionTimedDeath on 8:10 am on Jan. 24, 2002

You could:

Get a digital stopwatch that counts down or an alarm clock or whatever.

Connect a wire to the clock ground and a diode (cathode out!) to the sounder output.

Stick an an electrolytic capcacitor across the wire and cathode, along with a small ceramic one.

Put one end of a 10k resistor onto the cathode and
the other to the (b)ase of a transistor. Connect the collector to the +V battery.

The output is between the emitter and ground.

The capacitor should hold charge for long enough to
do whatever you want.

In theory of course.

If a QUALITY output is needed then another circuit will be needed. If you’re just driving a relay then it should do.
Remember to put a reverse biased diode across the coil otherwise the back EMF will kill the transistor.

This is untested of course. Someone try it!

— Posted by balor on 2:50 pm on Jan. 29, 2002

I presume that using the same principle in linking an alarm output with a Thyristor it would work with a mobile phone.I remember a mobile was used to detonate a bomb here a couple of years ago and the cops went hairwire about it.They thought that it was next generation remote detonation technology.Seems to me like that it is just an expensive remote trigger but the plus is that you can detonate the bomb from any part of the world depending on coverage of course.Any more ideas welcome.

— Posted by Hergor on 5:46 pm on Jan. 30, 2002

Quote: from balor on 2:50 pm on Jan. 29, 2002
Seems to me like that it is just an expensive remote trigger but the plus is that you can detonate the bomb from any part of the world depending on coverage of course.

well, expensive? in germany you can get mobile phones for just one euro (in connection to a one-year contract, but who cares if the mobile is ‘discarded’ after one single use? – giving fake id anyway)

— Posted by Zambosan on 9:23 am on Jan. 31, 2002

Many electronics hobby catalogs will sell a kit for a simple digital timer, usually based on MSI logic chips. Binary-coded-decimal counters are the simplest to interface a display to, as the 4-bit BCD outputs can be decoded to a 7-segment display with an inexpensive chip (4511 is a common part #). If the counter is binary by nature, you can squeeze more time resolution out of the same amount of hardware, but the output is not so easily displayed, since each 4 bit nybble is counting in base 16 instead of base 10. Even just directly displaying the bits on an led bar graph is useful, though… arrange the outputs to drive a tri-color one with the red LED’s corresponding to the least significant bits and the greens to the most significant bits, and you’ll get a color indication at a glance; if any green is showing, you still have a lot o’ time, etc.

I used to have a PALASM file for a 14-bit binary counter for a PAL22v10 device with binary outputs; I etched some pretty simple little boards that drive the counter with a 555 circuit with a variable resistor to tune the delay from about 20 sec. to 8 minutes or so. A flashing LED would give you an indication of the frequency. On power-up, the device would be in an idle state, allowing you to get everything ready. The state machine would wait for a high on one of the inputs before couting; I had a quick ‘n dirty flush-mount PC button & resistor combo for this input, debouncing wasn’t required since there was only one state transition dependent upon the input.  Output was a contact closure via a little 6v relay (also required a small single-NPN current amplifier with a snubber diode across the relay coil), brought out to a dinky terminal block at the board bottom. The chip logic also accepted two logic inputs for boobytrapping; the board circuitry was such that one input would keep the device “happy” with a closed circuit, the other with an open circuit. If the open circuit was closed (e.g. a pushbutton or tripwire), the output would fire prematurely, same deal if the closed circuit was opened. The closed circuit was disabled by default via a board jumper that could be removed if you wanted to use the trap inputs. I never used ’em incidentally, I made 3 of the boards and just used them for testing HMTD caps… I never really had any intentions to harm anyone. The logic was powered by a 9v, and the charge could be initiated by a 6v battery to ensure enough current for the ignitor; I just shelled out the $$ for Estes ignitors rather than dicking around with improvised ones.

Incidentally, a thyristor or SCR will require a decent amount of base current to get it to “lock” into an on state. Logic outputs don’t have that kind of drive capability, so another stage is required. Another less expensive proposition than a cellphone; use a pager. The vibration output is usually steady, not an oscillation like the piezo alarm. The vibration is just caused by a little motor driving an off-center mass. Tap into the ground and use the motor power to drive a relay instead (disconnect the motor of course).

— Posted by irritant on 4:14 pm on Feb. 1, 2002

Hergor::Could you send me those plans please. I am currently studing counters in school that triger other curcuits. When Ive got  a good design ill post it here::>

— Posted by johnny 99 on 11:57 pm on Mar. 14, 2002

I have a book from paladin press called smart bombs that has just what you are looking for a low voltage sensing relay that you can connect to any kind of digital clock/timer with an alarm to fire your demo. unfortunately i have no way to post it. I could try to describe it or send it to you snail mail whatever if you are interested.

— Posted by Gold Knight on 10:11 pm on Mar. 20, 2002

I was wondering if you could send me the plans for the timer that you were just talking about.

— Posted by johnny 99 on 2:00 am on Mar. 21, 2002

Check back in a couple of days, I will try to have them posted here.

— Posted by Gold Knight on 5:48 pm on Mar. 21, 2002


— Posted by trowe on 12:05 pm on Mar. 22, 2002

this aint no digital, but it works wonders…

    Timer delays, or “time bombs” are usually employed by an individual who
wishes to threaten a place with a bomb and demand money to reveal its location
and means to disarm it.  Such a device could be placed in any populated place
if it were concealed properly.  There are several ways to build a timer delay.
By simply using a screw as one contact at the time that detonation is desired,
and using the hour hand of a clock as the other contact, a simple timer can be
made. The minute hand of a clock should be removed, unless a delay of less
than an hour is desired.

           ___________________________________  to igniter      from igniter
           |                                  |
           |               12                 |      :            :
           |         11           1           |      :            :
           |                                  |      :            :
           |     10                   2       |      :            :
           |                 o…………….|……:            :
           |                                  |                   :
           |   9                         3    |                   :
           |                                  |                   :
           |                                  |                   :
           |    8                      4      |                   :
           |                        o………|……             :
           |          7             5         |     :             :
           |                 6                |     :.+…..-…..:
           |__________________________________|     __|_____|
                                       |           |
                                       |  battery  |
         o – contacts                  |           |
         ….. – wire                  |           |

    This device is set to go off in eleven hours.  When the hour hand of the
clock reaches the contact near the numeral 5, it will complete the circuit,
allowing current to flow through the igniter or squib.

    The main disadvantage with this type of timer is that it can only be set
for a maximum time of 12 hours.  If an electronic timer is used, such as that in
an electronic clock, then delays of up to 24 hours are possible.  By removing
the speaker from an electronic clock, and attaching the wires of a squib or
igniter to them, a timer with a delay of up to 24 hours can be made.  To utilize
this type of timer, one must have a socket that the clock can be plugged into.
All that one has to do is set the alarm time of the clock to the desired time,
connect the leads, and go away.  This could also be done with an electronic
watch, if a larger battery were used, and the current to the speaker of the
watch was stepped up via a transformer.  This would be good, since such a timer
could be extremely small.  The timer in a VCR (Video Cassette Recorder) would
be ideal.  VCR’s can usually be set for times of up to a week.  The leads from
the timer to the recording equipment would be the ones that an igniter or squib
would be connected to.  Also, one can buy timers from electronics stores that
would be ideal.  Finally, one could employ a digital watch, and use a relay, or
electro-magnetic switch to fire the igniter, and the current of the watch would
not have to be stepped up.

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