Relacement for SCR

When I started this thread it was more out of necessity. The time spent playing with this circuit has been well spent. No it isn't an SCR. Never meant to imply that. However the latching feature of an SCR was the idea behind it all and it does that quite well once you figure out the correct values. This circuit has the added benefit you mentioned of dual gate as well as active turn off. Over all a great learning experience for myself. Never realised how much I had forgotten. Thanks for all the good answers guys.
 
I consider myself fairly advanced, but I am in basics because there are still basic things I do not know or forgot. I designed parametric tone controls and a bulletproof relayless protection syustem for an amp many years ago and quite honestly I could not do it again.

This was a beauty. the bass control turnover was variable from 48 to 480 Hz and has a range of +/- 18 dB. It used a different scheme than the regular Baxandall or whatever using the feedback loop, it mixed. That means the turnove frequency stayed rock solid at any level of boost or cut.

The protection, well there was DC on the output but it was bridged. ANY short would shut the thing down so fast a relay could never do it. What's more, you could connect the speaker to a car battery and it would burn the wires off.

If pressed I could do it again I guess, but I am not really impelled to do so. I think cars should not even have stereos. Just radios.

Things have changed, I have changed. I used to build custom amps for cars, and I mean from scratch. Of course I have been one upped by the more recent technology, but whether or not, I simoply don't realy want to do it anymore.

I am actually looking for something to do. To design again. Tell me your needs. Some things I can do, alot of things I can't. But even now I am learning.

In fact, I have a math tutor. He ants to learn electronics and I want that higher math, the lack of which has held me back somewhat. when I design I sometimes have to take a shotgun approach. Overbuild things. I think that is good. I think caascade failures are bad and my approach makes them less likely.

But still, I need to learn more, even at my age. Even those 80 year old fucks in SED are still learning.

The best part of it is doing something useful with it.
 
In article <2c7a2d04-36f2-4738-9d1f-ff28274e8ff4@googlegroups.com>,
strmbrgr2@hotmail.com says...
When I started this thread it was more out of necessity. The time spent playing with this circuit has been well spent. No it isn't an SCR. Never meant to imply that. However the latching feature of an SCR was the idea behind it all and it does that quite well once you figure out the correct values. This circuit has the added benefit you mentioned of dual gate as well as active turn off. Over all a great learning experience for myself. Never realised how much I had
forgotten. Thanks for all the good answers guys.
Click to expand...

now stick that circuit in a freezer box and see if it works when it gets
below freezing,,

Jamie
 
At this point I have gotten what I needed out of it. The final alarm design does not use the SCR. I used two 555 timers to perform the functions I needed. Have proto'd it and it works great. Has approx 4 minute alarm with 26 second hold off for entry. 12 vdc 26 ah battery powered. 2. 30 watt horn external sirens plus 6 internal siren annunciators. If they do happen to gain entry it will be so annoying hopefully they will not want to hang around. Has home/away mode as well. Remote controlled using key fob and receiver. Several traps as well that look like they would disable alarm which in fact set it off.
 
Now there's an idea. Put all the sirens and shit inside the protected area. This will hurt their ears, and maybe cause hearing damage. What's more they won't hear you creeping up on them with your gun.

Know what ? How about strobe lights in the area as well. They are usually not going to be all that familiar with the floor plan and shit, so this will trip them up. If they are familiar with the floor plan, somoene has the wrong friends.
 
Not sure whether you were being sarcastic or not. I do in fact have an strobe external to alert police. The main idea of an alarm is to deter would be thieves. If they aren't deterred sufficiently I figured it would be prudent to annoy the shit out of them and maybe change their minds by making it uncomfortable to remain. I figured 6 of the 105 db sirens in unison inside the house would be enough. The location is out in the country and has been burglarized 3 times. They have also hit numerous other homes in the area recently. It is family and they are frankly fed up with it. Just got info that the police have identified persons of interest. Too late for my brother but at least he is taking steps to thwart future attempts.
 
OK. One more question for all who lurk. I am using 555 monostable. While triggered I have found that a new trigger has no effect. It will not accept a new trigger until it has timed out. I need to extend the timing period upon receipt of additional triggers. I was thinking of using a transistor to dump the timing cap charge so it will continue timing. Would it work and if so would an NPN work or should I use MOSFET? Thanks in advance.
 
Great. I thought I remembered seeing it done somewhere previously. I happen to have a few 2222s. Will give it a try today and report back findings. Thanks for the response. You guys are really a great resource. Very nice to find a group with the same passions for electronics as I.
 
On Mon, 16 Feb 2015 00:26:49 -0800 (PST), "Ron M."
<strmbrgr2@hotmail.com> wrote:

>OK. One more question for all who lurk. I am using 555 monostable. While triggered I have found that a new trigger has no effect. It will not accept a new trigger until it has timed out. I need to extend the timing period upon receipt of additional triggers. I was thinking of using a transistor to dump the timing cap charge so it will continue timing. Would it work and if so would an NPN work or should I use MOSFET? Thanks in advance.

Yes that would work. Your timing may be different than normal 555 ops
because you are taking the charge down to whatever VCEsat is for the
transistor you choose to use versus the 1/3 V+ the 555 normally works
with.

Either should work. I've used 2N2222s and 2N7000's (N channel mosfet)
 
I think NPNs hate me. Used a 2N2222 and it screws up the timing. Never times out. Tried diode isolation and several different permutations with no success. Will try Mosfet next. After that I am thinking of just using small relay to short the timing cap. At least I know that will work.
 
On 2015-02-17, Ron M. <strmbrgr2@hotmail.com> wrote:
> I think NPNs hate me. Used a 2N2222 and it screws up the timing. Never times out.

have you got the pins the right way round?

--
umop apisdn
 
>"have you got the pins the right way round? "

I hearya on that one. Once you get used to ECB all the time...
 
On Tue, 17 Feb 2015 11:41:22 -0800 (PST), "Ron M."
<strmbrgr2@hotmail.com> wrote:

>I think NPNs hate me. Used a 2N2222 and it screws up the timing. Never times out. Tried diode isolation and several different permutations with no success. Will try Mosfet next. After that I am thinking of just using small relay to short the timing cap. At least I know that will work.

Look up the data sheet for the actual manufacturers part, not all use
the common EBC pinout. You shouldn't have to resort to mosfets if you
don't have any handy.

AND I recommend one of those multitesters that also checks transistor
gain. Most are useless for mosfets as a rule, but it tells you
something about the quality of the parts you have, and if the pinout
you are using is the pinout of the part.

Any multimeter with a diode test (nearly all) function will also tell
you the pinout.

555's can also stay on if the reset line is pulled low, but that makes
a short glitch on the output after the end of each timing cycle, and
you'll get a part of a cycle if you release the reset line while it is
timing.
 
I checked and the leads were correctly oriented. Will continue working on that problem. You mentioned the 555 output producing momentary high when reset is taken low. I am using the reset line to control enable/disable. Seems to work rather well. Using +5vdc out from wireless via level shift to control reset on 3 555's. One for PIR input. One for delay entry and last for alarm output. The closed loop triggers entry and alarm. Entry trigger gnd is sourced from output of alarm timer so once they are triggered entry is not allowed to retrigger until alarm times out. This along with alarm cap charge deletion is what keeps it alarming with continuing triggers. That is the Away mode. In the Home mode the entry delay and PIR are disabled with just the perimeter loop active. Any intrusion produces instant alarm giving occupant more time to respond to threat. Any way I have gone much deeper into its operation than needed but figured you guys would tell me if I have it wrong. Will continue to work on the thing cap issue.
 
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