photoresister circuit...

R

RAB

Guest
Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

Thanks,
RABMissouri2008
 
On Fri, 31 Oct 2008, RAB wrote:

Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

You need a latch of some sort. An scr would do it, once triggered it
Click to expand...
continues to conduct until the DC voltage is removed from the anode.
In the old days, you'd apply voltage to a relay that not only switched
whatever you wanted, but also had an extra set of contacts that would
keep the relay coil energized. You can make latches with a couple of
transistors. Or of course, an actual IC flip-flop.

Michael
 
"RAB" <rabmissouri@yahoo.com> wrote in message
news:93329dd3-d91d-4930-986d-ac440f710b53@b31g2000prf.googlegroups.com...
Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

Thanks,
RABMissouri2008
Click to expand...
There are some basic circuits on the web if you know where to look, one good
place to look is in the handbooks for the Philips EE kits - the EE8/20 and
EE1003/1004 books have some good examples of LDR circuits.

Most of the books are in a variety of languages so make sure to pick English
or multi-lingual downloads.
 
"ian field" <gangprobing.alien@ntlworld.com> wrote in message
news:I_LOk.204312$dG5.54957@newsfe14.ams2...
"RAB" <rabmissouri@yahoo.com> wrote in message
news:93329dd3-d91d-4930-986d-ac440f710b53@b31g2000prf.googlegroups.com...
Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

Thanks,
RABMissouri2008

There are some basic circuits on the web if you know where to look, one
good place to look is in the handbooks for the Philips EE kits - the
EE8/20 and EE1003/1004 books have some good examples of LDR circuits.

Most of the books are in a variety of languages so make sure to pick
English or multi-lingual downloads.
Click to expand...
Oops - I clipboarded the link then forgot to paste it on my reply.

Here it is: http://ee.old.no/library/
 
On Nov 1, 5:43 am, RAB <rabmisso...@yahoo.com> wrote:
Hello,

I want to make an inexpensive circuit that uses a photoresister.   I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer.  My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

Thanks,
RABMissouri2008
Click to expand...
Hi RAB,

May be something like this would work for you:



+----------------+--------+-------+ 9V
| NORMALLY | | |
| CLOSED o| | .-.
| PUSH BUTTON |==|> - | |
.-. SWITCH o| 1n4148^ | |buzzer
| | | | '-'
| |LDR | +-------+
'-' .-. |
| | | |/
| 1K| | +-| NPN
| ___ '-' | |>
+--|___|---+ | | |
| 330 | | | |
| | SCR V | == .-. | - | GND
| | +----/| |
1K| | | +----+
'-' | .-.
| .-. | |
| | | | |1K
| 1K| | '-'
| '-' |
| | |0V
=== === == GND GND GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

I only did it on paper as my circuit simulator doesnt simulate it
properly.
The original circuit is in courtesy of ehsjr. I just modified it a
bit to work for your need. I think it should work with any low power
SCR.

Allen
 
On Fri, 31 Oct 2008, Bill Bowden wrote:

On Oct 31, 2:15 pm, Michael Black <et...@ncf.ca> wrote:
On Fri, 31 Oct 2008, RAB wrote:
Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

You need a latch of some sort. An scr would do it, once triggered it
continues to conduct until the DC voltage is removed from the anode.
In the old days, you'd apply voltage to a relay that not only switched
whatever you wanted, but also had an extra set of contacts that would
keep the relay coil energized. You can make latches with a couple of
transistors. Or of course, an actual IC flip-flop.

Michael

Another approach is a 555 timer in the one-shot mode and manually
reset it. But I like the scr idea.

It can just be used as a set-reset latch. Drop pin 2 to ground, and
Click to expand...
that sends the output high, but since nothing is resetting it (ie pin
7 isn't connected to anything) the output stays high. Then to reset
it, ground pin 4 (which is the reset pin).

The 555 does have the advantage that it's available and operates
over a reasonably wide range of voltage.

Michael
 
On Oct 31, 2:15 pm, Michael Black <et...@ncf.ca> wrote:
On Fri, 31 Oct 2008, RAB wrote:
Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

You need a latch of some sort. An scr would do it, once triggered it
continues to conduct until the DC voltage is removed from the anode.
In the old days, you'd apply voltage to a relay that not only switched
whatever you wanted, but also had an extra set of contacts that would
keep the relay coil energized. You can make latches with a couple of
transistors. Or of course, an actual IC flip-flop.

Michael
Click to expand...
Another approach is a 555 timer in the one-shot mode and manually
reset it. But I like the scr idea.

-Bill
 
"RAB" <rabmissouri@yahoo.com> wrote in message
news:93329dd3-d91d-4930-986d-ac440f710b53@b31g2000prf.googlegroups.com...
Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

Thanks,
RABMissouri2008
Click to expand...

Why not just connect a lamp in parallel with the buzzer and let that shine
on the 'photoresister'?

Chris
 
On Fri, 31 Oct 2008 14:43:32 -0700 (PDT), RAB <rabmissouri@yahoo.com>
wrote:

Hello,

I want to make an inexpensive circuit that uses a photoresister. I
know how to use the photorestor as a voltage divider that can trigger
a transistor which can turn on a buzzer. My question is...how could I
make the circuit such that the buzzer stays on even when the
photoresister goes to its reset state?

Thanks,
RABMissouri2008
Click to expand...
Try this:


5V ---o-------------------o------------o-------------.
| | | |
| .-. .-. |
,---. | |10k | |10k |
| X | LDR | | | | |
'---' '-' '-' |
| | | |<
| o------------)----o------| PNP
A o------->|----o-----)------------o | |\
| | | | .-. |
| .-. | | | |100k |
| 100k| | | | | | | .---|
| | | | | '-' '-|+ |
| '-' | | | .-| |
| | |/ \| | | '---|
| .-----o---| NPN NPN |--' | Buzzer
.-. | | |> <| |
| |R | | | | |
| | |+ | | | |
'-' 1nF--- o | | | |
| --- |=| | | |
| | o | | | |
| | | | | |
| | | | | |
GND --o-------o-----o-----o------------o-------------'

Reset Push Button
Normally Open

Choose R so that point A is <= 1V in the dark

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The LDR will decrease in resistance as it gets lighter. So, point A
will increase in voltage until the 'flip flop' flips over and the
buzzer starts to buzz. The 1nF cap is there to start it in the right
state. The push button will reset the thing so the buzzer is off. So,
if you don't care what state it starts in, you can omit the capacitor,
and just reset it with the reset button. It should work with a 9V
battery too, but remember to adjust the resistor R so that point A is
less than 1V while it should be off.

Regards,
Bob Monsen
 
Thanks for all the responses. Since I don't have an SCR handy (I will
have to order one) I got something to work by using a PNP and an NPN
transistor wired like the diagram at the following link.
http://en.wikipedia.org/wiki/Silicon_controlled_rectifier This is
similar to the circuit Bob Monsen shared.

RABMissouri2008
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top