Device that blocks a signal, 200426

[AllenPitts]

Hello ElectroTech,
Have designed a circuit and a PCB that sends the signal from a PIR sensor (motion detector) and
triggers a 555 timer to turn on some LEDS for about a minute. I call the circuit P5L (PIR to 555 to LEDs).
It has taken about month to design the schematic, prove the circuit logic with a breadboard, and
design and order the PCBs.

The plan is to use several P5Ls to, instead of turning all lights on stairway at once, light up the
staircase two or three treads at a time so that the system reacts to the movement of the walker. I saw
something similar at a staircase at the Perot Museum in downtown Dallas.

The plan is to have the system work differently depending on whether the walker is going up the stairs
or down the stairs. Or stated more formally
System Requirements:
Use Case One (going up): When sensor S6 is triggered the LEDS above (LED L7.1 and L7.2) are turned on
if LEDs below (L5.1 and L5.2) are on.
Use Case Two (going down): When sensor S6 is triggered the LEDS below (LED L5.1 and L5.2) are turned on
if LEDs above (L7.1 and L7.2) are on.

Sensor S6 is used in the requirements as an example to illustrate that the lights below a sensor would
be activated by movement down the stairs and lights above above a sensor would be activated by movement up
the staircase. The exception is sensors S1 and S8. There are no lights below S1 or above S8 and so S1
has no sensitivity to another set of lights. S1 simply turns on LEDs L1.1, L1.2 and L1.3. And similar for S8.

In Use Case One (going up) S6 is triggered and sends signals to the transistors operating both LEDS L7 and L5.
But a device is needed to detect the signal from the S6 PIR to the L5 lights, and if L5 is on,
the device blocks the PIR signal from going to the transistor operating the L5 LEDs.
In Use Case Two (going down) S6 is triggered and sends signals to the transistors operating both LEDS L7 and L5.
But a device is needed to detect the signal from the S6 PIR to the L7 lights, and if L7 is on,
the device blocks the PIR signal from going to the transistor operating the L7 LEDs.

So the device is like transistor in reverse. That is, a transistor uses a signal at the base to allow current to flow.
What is needed that, instead of closing a circuit and allowing current to flow, the device opens a trace
and prevents a current from flowing.

Is there such a device?

Thanks.

Allen in Dallas

 

[eTech]

Hi

Questions:
1. Is only one person allowed to use the stairs at a time?
2. Is a person allowed to reverse motion on the stairs.

eT

 

[AnalogKid]

Doing this in random logic, without a microcontroller, is going to take a *lot* of logic devices. I rarely recommend a uC because of the software development overhead, but in this case I think it is worth it. You have 8 inputs and 16 outputs. An Arduino can handle this with a small amount of external logic. A uC also would give you the capability of tracking one body moving in each direction at the same time, including when they pass each other. Not beginner-level software, but an indication of what is possible.

ak

 

[eTech]

Doing this in random logic, without a microcontroller, is going to take a *lot* of logic devices. I rarely recommend a uC because of the software development overhead, but in this case I think it is worth it. You have 8 inputs and 16 outputs. An Arduino can handle this with a small amount of external logic. A uC also would give you the capability of tracking one body moving in each direction at the same time, including when they pass each other. Not beginner-level software, but an indication of what is possible.

ak

I agree.

 

[gophert]

Although it would be fun to see the array of logic chips or P5L modules all wired up, you'll save yourself a huge headache doing it with a microcontroller. Writing all the permutation cases in code will be much easier than running all of the permutations with wires.

 

[Nigel Goodwin]

Likewise, it's an obvious case for a microcontroller, which will make it much simpler, much cheaper, and able to perform much more functions (if required).

 

[rjenkinsgb]

Coincidentally, I was thinking about a similar system a few days ago, to control lights for a path across the front of my house.
As a programmer, using a microcontroller is simplest - but I was considering discrete logic possibilities as well.

The simplest device to use is a "D Type" flip flop such as a 4013. A D type captures the state of the D input each time the clock input switches from low to high.

Feed the D input from the timer active signal in the sensor "behind" the present one and Clock from the sensor in the unit the 4013 is in.

If the one behind it was already on when it is triggered, the Q output will be high; otherwise it will be low. Connect reset to the local timer circuit such that the 4013 is reset when the time expires.


Use 4013 Q to feed (eg. via a diode / diodes) to the light power switch circuit in the one (or two / three) "ahead" of the current location; not the timer/PIR trigger; that would cause every light ahead to come on.

That circuit needs duplicating with before/after swapped over for the other movement direction. Each 4013 has two D types in it so one IC per sensor+lamp unit. There is very little needed other than a 4013 per unit.

4000 series ICs are made by many companies with different prefixes, eg. CD4013, HEF4013 etc.
This is the data for one example:

https://www.homepages.ed.ac.uk/alister/P03/CD4013.pdf