Help with using a PIR to trigger a NE555

Bernard

Joined Aug 7, 2008
5,784
Just replace the 5V relay with the 12V relay. Would help to know coil resistance or coil current to figure 2N2222 new base resistor.
 

AnalogKid

Joined Aug 1, 2013
10,176
Given that everything is running on 12 Vdc, there is no explicit need for relays. Do you really want some in the design, or would small transistors (2N4401, 2N2222, 2N7000, etc) be ok?

ak
 

AnalogKid

Joined Aug 1, 2013
10,176
Late to the party, working on a slightly different approach. Can you post a link to the PIR module you are using? There are lots on ebay, but I didn't see one that looks like your image in post #1. Is that a true PIR sensor, or an infra-red object sensor?

Thanks.

ak
 

AnalogKid

Joined Aug 1, 2013
10,176
First pass at a schematic. This uses a CMOS logic gate package to form a boxcar or pulse-stretcher type of monostable. Unlike a 555, this circuit's pulse ends no matter which state the SENSE-1 input is in, so the trigger signal does not have to be differentiated.

R1-R2-C1 set the red LED on-time. R2 should give approx 10-30 sec range.

A white LED has a forward voltage of around 3 V to 5 V, so you cannot run four of them in series on a 5 V source, or probably even on a 12 V source. This is why they are broken up into two strings. The POINT switch powers them directly, eliminating one relay or switching transistor.

D1-D2-D3 form a cute switching system that controls two different LEDs with only one transistor. In the normal case, Q1 is on, the green LED is on, and the white LEDs might be on depending on the state of the POINT switch. Because the forward voltage of a typical green LED (2.1 V) is less than the combined forward voltages of a typical red LED (1.8 V) and a small signal diode (0.6 V), the red LED is off, effectively "shorted out" by the green LED. When SENSOR-1 is activated, Q1 is turned off, the green LED is disconnected from GND, and R3 sources current through the red LED.

Depending on the SENSE-1 vs SENSE-2 timing, I might have to add another 1N914 diode across R1-R2 to shorten the recovery time.

*** R4 and R5 should be 390, not 390K.

ak

ps. Another approach is to *** eliminate all ICs *** and use three 2N7000 transistors to do everything.

Train-Lights-1-c.gif
 
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Thread Starter

AllisonAmg

Joined May 18, 2020
71
First pass at a schematic. This uses a CMOS logic gate package to form a boxcar or pulse-stretcher type of monostable. Unlike a 555, this circuit's pulse ends no matter which state the SENSE-1 input is in, so the trigger signal does not have to be differentiated.

R1-R2-C1 set the red LED on-time. R2 should give approx 10-30 sec range.

A white LED has a forward voltage of around 3 V to 5 V, so you cannot run four of them in series on a 5 V source, or probably even on a 12 V source. This is why they are broken up into two strings. The POINT switch powers them directly, eliminating one relay or switching transistor.

D1-D2-D3 form a cute switching system that controls two different LEDs with only one transistor. In the normal case, Q1 is on, the green LED is on, and the white LEDs might be on depending on the state of the POINT switch. Because the forward voltage of a typical green LED (2.1 V) is less than the combined forward voltages of a typical red LED (1.8 V) and a small signal diode (0.6 V), the red LED is off, effectively "shorted out" by the green LED. When SENSOR-1 is activated, Q1 is turned off, the green LED is disconnected from GND, and R3 sources current through the red LED.

Depending on the SENSE-1 vs SENSE-2 timing, I might have to add another 1N914 diode across R1-R2 to shorten the recovery time.

*** R4 and R5 should be 390, not 390K.

ak

ps. Another approach is to *** eliminate all ICs *** and use three 2N7000 transistors to do everything.

View attachment 209010
Interesting.... I hadnt considered using other than NE555 as i am not very electronic savey, i am old school using relays. This seems a 'cheaper' option as i will need a lot of these modules. I will have to build a prototype on breadboard to see if it meets the requirements. As i dont have either a 2N7000 or CD4093 i will have to order a couple of each.

kindest
Allison



kindest
Allison
 

ericgibbs

Joined Jan 29, 2010
16,830
bore da Allison,
As already pointed out, as the White LED require approx 3.2V forward voltage drop, you cannot drive 4 in series from 12V, use two pairs in parallel.
E
 

AnalogKid

Joined Aug 1, 2013
10,176
If you have other parts, the circuit can be adapted. NPN's such as 2N4401, 3904, 2222, etc? PNP's such as 2N4403, 3906, 2907, etc? Logic chips: 74xx14, 00, 02, 32, etc? 555: do you have bipolar (LM555, NE555) or CMOS (LMC555, etc.)? I probably can do it with a 555 version with a PNP transistor if you have those parts already.

1. Can you expand on the timing between the two SENSE signals? As I understand things, both SENSE signals go low when triggered by an object, and S2 always is triggered *after* S1. Is this correct?

2. If so, then does S1 release (return high) always *after* the timer has finished its 10-30 second interval, *always* before, or sometimes either one?

3. If S2 has been triggered, does it return high *always* before the next triggering of S1? Or might S1 go low again while S2 still is low?

4. Does the POINT switch have to switch 12 V, or can it be connected to GND?

5. If the number of white LEDs can be reduced from 4 to 3, or increased to 6, things happen.

Depending on what the signals do and what parts you have, there are lotsa combinations that will work.

ak
 
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