Help: Circuit Design 4in NOR Gate

[eminence]

frs10c-03

I own an Alfa Romeo 75 car and I have fitted an alarm. Unfortunately Alfa decided to make the doors switches opposite to usual. When the doors are open they supply 0v GND (ground/negative) and when shut they supply 12v GND. So this makes it difficult to hook up to my alarm as it wants a 12v GND or 12v POS (positive) supply when the doors are open.

So not being that savy with electronics I figured I could get by with 4 relays (with NO/NC terminals), one for each trigger wire. I could not use one as there would still be 12v supplied if the other doors where shut and only one was opened. I rigged these up but as you would expect they chewed through the cars battery power pretty quickly as the coils were nearly always active because as you realise doors spend most of their time shut!

I went to a local electronics shop (JayCar) in Geelong, Australia and the person behind the counter recommended the following circuit layout.


(File also attached)

I have put his suggestion together, but I am not getting the reaction I had hoped for. The basic idea of the above circuit is that if door switch 1 or 2 or 3 or 4 are not switched/pulled/toggled/on/down/together then the NOR gate will tell the transistor to switch the relay on or off. Where the lamp is hooked into the above circuit the alarms positive door trigger wire would be hooked up in the actual application.

I hope that I have given you enough information to help me come up with a circuit that works.

Thanks in advance,
Simon

 

[sztibi82]

relay frs10c-03

Hi
I didnt understand well, but i think you get the desired connection using an or gate and not an or gate.

 

[nicleo]

frs10c-03 dc12v 3a

I own an Alfa Romeo 75 car and I have fitted an alarm. Unfortunately Alfa decided to make the doors switches opposite to usual. When the doors are open they supply 0v GND (ground/negative) and when shut they supply 12v GND. So this makes it difficult to hook up to my alarm as it wants a 12v GND or 12v POS (positive) supply when the doors are open.

I also did not quite get your point. However, I will try to understand. In my opinion, the circuit of the each door switch is like the one shown in Figure 1. Therefore,

When SW1 is OPEN, Vsw1 = 0V
When SW1 is CLOSE, Vsw1 = 12V


The requirement of the alarm circuit:

When the door switch (SW1) is OPEN, the required input is 12V
When the door switch (SW1) is CLOSE, the required input is 0V


If the scenario above is correct, Vsw1 is connected to a NOT gate. Then, all the switch signals (Vsw1, Vsw2, Vsw3, and Vsw4) are connected to a OR gate. The output of the OR gate is connected to the BASE of the transistor through a resistor. Pls update if I'm wrong.

 

[eminence]

c557c pdf

Hi
I didnt understand well, but i think you get the desired connection using an or gate and not an or gate.

They only had NOR gates at the shop.

Thanks,
Simon

 

[eminence]

c557c transistor

If the scenario above is correct, Vsw1 is connected to a NOT gate. Then, all the switch signals (Vsw1, Vsw2, Vsw3, and Vsw4) are connected to a OR gate. The output of the OR gate is connected to the BASE of the transistor through a resistor. Pls update if I'm wrong.

Vsw1 is connected to a NOR gate input which then ouputs to the base of a transistor through 100k resistor.

Thanks,
Simon

 

[nicleo]

12v nor gate

Vsw1 is connected to a NOR gate input which then ouputs to the base of a transistor through 100k resistor.

Comment as shown in figure.

 

[eminence]

circuit design of nor gate

Your second diagram looks pretty close. But there are no resistors between the door switch and the GATE. The circuit input is also GROUND not +12v.

Thanks,
Simon

 

[eminence]

12v dc nor gate

Vsw1 is connected to a NOR gate input which then ouputs to the base of a transistor through 100k resistor.

Comment as shown in figure.

I am sorry but I do not understand what you mean by floating when all switches are open?

Thanks,
Simon

 

[nicleo]

design simple if gate for 12v circuit

Well, I think I got your point now:

When door/switch is OPEN, the output signal from the switch is 12V.
When door/switch is CLOSE, the output signal from the switch is 0V.

Correct?

They only had NOR gates at the shop.

NOR gate is sometimes referred to as 'universal gate', because by utilizing a combination of NORs, all the other logic gates (NOT, AND, OR, NAND) can be formed.

I am sorry but I do not understand what you mean by floating when all switches are open?

When the switches are OPEN, the inputs to the NOR gate in your schematic are not pulled to HIGH (+5V) or LOW (GND). As the inputs do not have a 'known state', the output of the NOR gate might be wrong or not consistent or act strangely.

 

[eminence]

pnp transistor nor gate

I am sorry for all the confusion. But you still have not understood me fully.

When the door is closed the switches output is 12v GND. (The switch is closed at this point)

When the door is open the switches output is 0v GND. (The switch is open at this point)

Thanks again,
Simon

Well, I think I got your point now:

When door/switch is OPEN, the output signal from the switch is 12V.
When door/switch is CLOSE, the output signal from the switch is 0V.

Correct?

 

[nicleo]

using pnp transistor to implement nor gate

Ha Ha ... very confusing.

When the doors are open they supply 0v GND (ground/negative) and when shut they supply 12v GND.

Therefore when the door is open you get no GND, when the door is closed you get GND.

I am sorry for all the confusion. But you still have not understood me fully.

When the door is closed the switches output is 12v GND. (The switch is closed at this point)

When the door is open the switches output is 0v GND. (The switch is open at this point)

Conclusion:
When the door is closed the switches output is 12v GND. (The switch is closed at this point)
When the door is open the switches output is 0v GND. (The switch is open at this point)

By the way, you can form OR gate from NOR gates.

 

[eminence]

nor circuit using resistors and switches

I am sorry but I do not understand what you mean by floating when all switches are open?

When the switches are OPEN, the inputs to the NOR gate in your schematic are not pulled to HIGH (+5V) or LOW (GND). As the inputs do not have a 'known state', the output of the NOR gate might be wrong or not consistent or act strangely.

Oh OK so the GND signal from the door switch needs to be converted to +5v before the gate to make the gate change states. That would be one reason why its not working when supplied with GND.

Ha Ha ... very confusing.

When the doors are open they supply 0v GND (ground/negative) and when shut they supply 12v GND.

Therefore when the door is open you get no GND, when the door is closed you get GND.

I am sorry for all the confusion. But you still have not understood me fully.

When the door is closed the switches output is 12v GND. (The switch is closed at this point)

When the door is open the switches output is 0v GND. (The switch is open at this point)

By the way, you can form OR gate from NOR gates.

I thought they all meant the same thing???

By the way, you can form OR gate from NOR gates.

How can I create an OR gate from a NOR gate? Two NOR gates in series?
[EDIT]I notice that you edited your post to show a diagram of two NOR gates in series.[/EDIT]

Thanks for your patience,
Simon

 

[nicleo]

circuit design of nor

switchp[/u] figure]Therefore when the door is open you get no GND, when the door is closed you get GND.

All SAME???
I assume 'no GND' mean 12V. So, your comment in the 'switch' figure stated that when switches are 'open', we will get '12V'.

How can I create an OR gate from a NOR gate? Two NOR gates in series?

You need SIX NOR gates, each with TWO inputs. You will get a '4-input' OR gate if you combine the SIX NOR gates as shown in the attached figure.

 

[eminence]

frs10c-03 footprint

How can I create an OR gate from a NOR gate? Two NOR gates in series?

You need SIX NOR gates, each with TWO inputs. You will get a '4-input' OR gate if you combine the SIX NOR gates as shown in the attached figure.

Is it not possible to do it a bit more cheaply and use less circuit board space? Like have a NOR gate and then a transistor to inverse the signal from the NOR? I believe that is what the guy who made the orginal diagram was aiming for.

Thanks,
Simon

 

[eminence]

nor gate 12v switch

So I think what I should of said was that I need to design a circuit which when given 0v GND by one or two or three or four of the door switches will output +12v to a relay.

 

[atmaca]

frs10c-03 wiring

Out of your discussions Im going to point one issue.
May be this is the reason of malfunction of the advised circuit.
The input of the relay must be shunt with a reverse diode. Because reverse current from the relay can demage the switching transistor.

Thanks

 

[nicleo]

design dtl gates not

Out of your discussions Im going to point one issue.
May be this is the reason of malfunction of the advised circuit.
The input of the relay must be shunt with a reverse diode. Because reverse current from the relay can demage the switching transistor.

Agree... as a good practise, we need a diode across input of the relay.

So I think what I should of said was that I need to design a circuit which when given 0v GND by one or two or three or four of the door switches will output +12v to a relay.

Based on the truth table as shown in attached figure, the idea should work. May be you need to add pull up resistors before the input of NOR gates.

 

[eminence]

pnp nor gate

Out of your discussions Im going to point one issue.
May be this is the reason of malfunction of the advised circuit.
The input of the relay must be shunt with a reverse diode. Because reverse current from the relay can demage the switching transistor.

Thanks

Sorry forgot to put that in the diagram. I have a diode on the relay to stop damage to the transistor.

Simon

 

[eminence]

frs10c-03 circuit diagram

Out of your discussions Im going to point one issue.
May be this is the reason of malfunction of the advised circuit.
The input of the relay must be shunt with a reverse diode. Because reverse current from the relay can demage the switching transistor.

Agree... as a good practise, we need a diode across input of the relay.

So I think what I should of said was that I need to design a circuit which when given 0v GND by one or two or three or four of the door switches will output +12v to a relay.

Wait ...

How would you layout the schematic to achieve the desired result?

 

[eminence]

pnp nor gate

Out of your discussions Im going to point one issue.
May be this is the reason of malfunction of the advised circuit.
The input of the relay must be shunt with a reverse diode. Because reverse current from the relay can demage the switching transistor.

Agree... as a good practise, we need a diode across input of the relay.

So I think what I should of said was that I need to design a circuit which when given 0v GND by one or two or three or four of the door switches will output +12v to a relay.

Based on the truth table as shown in attached figure, the idea should work. May be you need to add pull up resistors before the input of NOR gates.

Q1 is indead a PNP transistor.

What are pull up resistors?

From what I can tell the gate is not going to change because the inputs are not +V, but I am not sure? Can the 4002 gate be changed with a GND signal fed to the inputs?

I am getting quite lost as most of this is more complex than I have really encountered before. The gates and truth tables I get because of my computing background. But when it comes to electrical component selection I get lost. I also have no idea really how to change the 0v in to +5v with a transistor?

Thanks,
Simon