# Anybody willing to help with a project please? -sequential logic problem

#### Razzle308

Joined Mar 17, 2016
49
Hi all.

I am putting some pressure pads into the path for my entrance way at home.
I have 10 pads and 4 correct ones. I want that one has to step on the correct ones in the correct order to actuate something.

I can build the circuit with my crude electronics knowledge out of relays but this doesn't give me the full functionality I want.

If anyone was willing to help me build a digital version it would be great. It is a little out of my lonesome depth.

Here is a flow chart of what i am trying to achieve.

regards Darren.

#### Phoenix P.A.

Joined May 10, 2016
3
Hi Darren, I can maybe help you with a microprocessor, I can write the code for U, this sort of thing does look like processor country, I use Atmel pieces, they cost about ZAR 40.00, I can also design the electronics if you like.

Regards

David

#### Razzle308

Joined Mar 17, 2016
49
Thanks so much
Well i was gonna mention not using arduino or such as i have never used one. I actually would love to play with one.
However.
How will such a circuit go with being powered up and down often? Will i talke time to "boot"? As this would not suit the application.
The application is .... ready for this?.....i am having gas tiki torches in my entrance. There will be 10 glass blocks in the path that act as pressure switches. When armed you will get a short period to find the correct blocks and step on the to turn the torches on. If you take too long or step on the wrong block it resets.

#### HW-nut

Joined May 12, 2016
97
A small micro like an Arduino would work very well for application. Boot up time is only an issue when an OS is used. The Arduino would be up an running milliseconds.

#### Phoenix P.A.

Joined May 10, 2016
3
No, I'm allergic arduino's, not that I've ever used or owned one, the device I propose for this is the Atmel ATtiny84, data sheet attached, I make 1 off PCB's , boot-up is in micro seconds, it runs on 5volts, so a mains transformer is needed + +, these torches, are they mains powered/triggered ?. I'm located in Nth West, South Africa.

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#### Razzle308

Joined Mar 17, 2016
49
I can step down from 12v so 5 is no issue.
The igniters and gas solenoids are all 12v.
I designed a nand circuit so when u press the correct block it changes colour too.

What do i need to program the chip? I presume i need a programmer.

I am in western australia.

#### Razzle308

Joined Mar 17, 2016
49
Ok...I'm a little excited about using a microcontroller. I've been googling

#### AnalogKid

Joined Aug 1, 2013
9,248
If you search for threads about digital locks on this and other fora you will find lots of circuits. Many of them take 2 to 4 simple CMOS chips.

LSI has been making single-chip digital lock chips for a few decades, and their parts work very well. Check out the LS7220.

http://www.lsicsi.com/prog_digitallocks.htm

ak

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#### Phoenix P.A.

Joined May 10, 2016
3

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#### hp1729

Joined Nov 23, 2015
2,304
Gotta wonder if a part with a 238 page datasheet and an external programmer is just a tad overkill for this project.

ak
The journey is what counts as well as the result. This would be a great "my-first-project" for a microcontroller, but I also suggest an CMOS IC version.

#### AnalogKid

Joined Aug 1, 2013
9,248
hp1729 - I think the schematic in post #11 needs work. Only one input clocks the tristate-feedback system, and there are no inputs from the bogus pads to reset the logic.

ak

#### Razzle308

Joined Mar 17, 2016
49
Hp1729. I cant seem to open pdf in here on my pad.

#### hp1729

Joined Nov 23, 2015
2,304
hp1729 - I think the schematic in post #11 needs work. Only one input clocks the tristate-feedback system, and there are no inputs from the bogus pads to reset the logic.

ak
Stepping on the correct first one starts a long timing interval in which the other three must be stepped on before time runs out. You are correct, I missed the action of stepping on the incorrect sensors. I missed the part where that was a requirement. Also I don't know if the sensors are active low or active high.
722x chips look good. Price and availability are a question.

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#### hp1729

Joined Nov 23, 2015
2,304
Hp1729. I cant seem to open pdf in here on my pad.
Sorry, the other option is an ORCAD file. Maybe someone can convert the PDF to JPG for us?

#### hp1729

Joined Nov 23, 2015
2,304
hp1729 - I think the schematic in post #11 needs work. Only one input clocks the tristate-feedback system, and there are no inputs from the bogus pads to reset the logic.

ak
Modify the previous design with the following. Stepping on any of the incorrect sensors kills the timing period timer.

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#### bertus

Joined Apr 5, 2008
21,364
Hello,

Here are the jpg's made from the PDF's.

Bertus

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#### Razzle308

Joined Mar 17, 2016
49
@hp1729

Does it reset on the correct block but incorrect order?

What is U3D?

The switches in the blocks are momentary - Will the blocks stay lit when pressed?

Maybe I should add some detail. When the timer is activated all the blocks light up. When the correct block is depressed it will change colour. ( i accomplish this with 2 nands when I get a second high signal.)

So the signal on the correct block needs to stay high until reset.

Hope I explained that ok.

#### hp1729

Joined Nov 23, 2015
2,304
@hp1729

Does it reset on the correct block but incorrect order?

What is U3D?

The switches in the blocks are momentary - Will the blocks stay lit when pressed?

Maybe I should add some detail. When the timer is activated all the blocks light up. When the correct block is depressed it will change colour. ( i accomplish this with 2 nands when I get a second high signal.)
View attachment 106053
So the signal on the correct block needs to stay high until reset.

Hope I explained that ok.
The details help. What should activate the timer? U3D is just an unused gate. Four gates to the chip.
With the new details my circuit won't work.
Your circuit. The top gate looks good. The bottom gate doesn't make sense to me. Why put one end to the resistor. It will always be low, making he output of that gate high all the time. The other input needs a pull up resistor before it will go high. Right now it is high when the switch is closed or floating, which could end up high or low.
Other question. Does the output of the sensor go high or low when stepped on?