DAC to ADC over single wire (SP4T)

[sellis]

Here is the situation. I have two 15' wires going to a location that has ground. At this location I have 4 momentary switches that I need to connect to 4 inputs on a PCM at the other end of the wire. Only need one closed switch at a time. If it was only three switches I could just send grounds back on the two wires and have the PCM decide the switch pressed.

Note the PCM can not measure resistance or voltage fast enough to just use resistors on the momentary switches.

So one wire needs to be supply voltage and other wire the signal. I was hoping to just purchase two boards that I could hook up as opposed to ordering all the components and building circuit boards. Everything I found until now has a two wire bus. Other option is to add resistors to the switches and have a circuit at the PCM to sort things out by resistance.

Is there a specific name for this kind of setup? Any direction/suggestions will be greatly appreciated.

Thanks!

 

[Pommie]

And PCM is what?

Mike.

 

[Mickster]

And PCM is what?

Mike.

I thought the same...
Pulse Code Modulation?
Powertrain Control Module?
Phase Change Memory?
Please Call Me?

Throw us a bone please sellis.
There's too many TLA's out there.

 

[ronsimpson]

DAC to ADC

?

You have 4 wires in a cable. One wire should be ground. There are 4 switches.
The PCM thing has 4 inputs.

Questions: can you program the PCM?
Example: (4 switches and 4 inputs that is simple) BUT (What if 4 switches and 3 inputs on the PCM and it takes some software to make it work)
Three inputs to PCM 111 (all inputs high = no switches closed)
………..(011= switch 1 closed)
...………(101=switch 2 closed)
….......(001=switch 3 closed)
………….(110)=switch 4 closed)
[could go to 7 switches)
This can be done by adding some diodes to the switches.

 

[sellis]

HaHa, PCM = programable control module (actual unit **broken link removed**)

You have 4 wires in a cable. One wire should be ground. There are 4 switches.
The PCM thing has 4 inputs.

I only have 2 wires to use. Ground is already at the location.
I am programing the PCM so can add any logic. Also PCM inputs can be high or low.

 

[Nigel Goodwin]

HaHa, PCM = programable control module

You'd do better actually using proper 'words' rather than making up your own acronyms, there are already a great number of acronyms that use PCM - not including the one you seem to have invented?. It's not even called a 'programable control module' on the page you linked to.

 

[sellis]

Sorry about the PCM thing. This is not my area of expertise. I will just call it a controller for now

With two wires I was thinking a simple circuits for a pair of switches on each wire...

S1 would activate both Controller inputs but S2 with a resistors will fail to activate second input.

Is something like this workable and if so are my schematics correct?

 

[DrG]

At this location I have 4 momentary switches that I need to connect to 4 inputs on a PCM at the other end of the wire. Only need one closed switch at a time.

https://ww1.microchip.com/downloads/en/devicedoc/01146b.pdf

Figure 9-1 (page 1-6) Would that work? You would not need the jumper part or the 5th GPIO (other side of diodes would be gnd).
This may be what post #4 is pointing out with the diodes and 4 GPIO.

 

[ronsimpson]

I only have 2 wires to use. Ground is already at the location.

I have two 15' wires going to a location that has ground.

It is not a good idea to relay on ground 15 feet away. There could be volts of difference between grounds. and noise.
Do you have power where the switches are?

 

[DrG]

It is not a good idea to relay on ground 15 feet away. There could be volts of difference between grounds. and noise.

Asking, not arguing...what kind of buffer or isolator https://www.analog.com/en/technical-articles/anatomy-of-a-digital-isolator.html could be added or ?

 

[sellis]

It is not a good idea to relay on ground 15 feet away. There could be volts of difference between grounds. and noise.
Do you have power where the switches are?

It is what I have to work with. The ground is a steel frame that surrounds everything and there is no high voltage or frequency anywhere within the steel frame so should be very little noise.

No power at sw, only two wires. If I need power then I need to use one of the wires for it.

 

[DrG]

Sorry about the PCM thing. This is not my area of expertise. I will just call it a controller for now

With two wires I was thinking a simple circuits for a pair of switches on each wire...
View attachment 119660
S1 would activate both Controller inputs but S2 with a resistors will fail to activate second input.

Is something like this workable and if so are my schematics correct?

I understand that I may not know too much about this and maybe that is why you did not acknowledge my earlier post - n/p but I have a couple of specific questions...that would help me understand and maybe learn something, if not provide you with a solution.

Your topic title is "DAC to ADC over single wire (SP4T). Can you explain why this has anything to do with DAC or ADC because it seems like it does not to me.

Does the SP4T in your title refer to simple momentary switches as you have drawn in your schematic or to an SP4T like this one.

How are the controller inputs configured? Which of the possibilities as described here (p3)?

Given how simple your schematic is, have you tested it?

Thanks.

 

[ronsimpson]

Here is a bad idea but maybe it will help.
This IC us used in garage door openers. Inputs A0-A7 are address so it will only talk to the receiver with the same address. AD8-AD11 are for switches. Normally Dout goes to a RF or IR transmitter. But could just be a wire. (needs power!)

I can not find the receiver IC now. It is about the same thing but AD8-AD11 are outputs.

There are many different versions of this. More/less switches.
I have used one wire to send power and data at the same time.
options:
Wire 1= power, Wire 2= Dout
Wire 1=power and Dout, Wire 2=ground.

 

[sellis]

I understand that I may not know too much about this and maybe that is why you did not acknowledge my earlier post - n/p but I have a couple of specific questions...that would help me understand and maybe learn something, if not provide you with a solution.

Your topic title is "DAC to ADC over single wire (SP4T). Can you explain why this has anything to do with DAC or ADC because it seems like it does not to me.

Does the SP4T in your title refer to simple momentary switches as you have drawn in your schematic or to an SP4T like this one.

How are the controller inputs configured? Which of the possibilities as described here (p3)?

Given how simple your schematic is, have you tested it?

Thanks.

I though I was looking for a DAC/ADC like https://www.aliexpress.com/item/32903378127.html on each end except uses a single wire bus. And SP4T because the 4 switches sort of act like a 4 pole rotary switch, only one active at a time.

I can configure the inputs any way needed. Note the inputs are slow to read voltage change though.

Circuit was more of a concept. I would be surprised if it worked

 

[sellis]

Here is a bad idea but maybe it will help.

Looks very interesting. One wire for 5v and the other for signal should work fine. Worth a try anyway.

Thanks!

 

[ronsimpson]

I though I was looking for a DAC/ADC like https://www.aliexpress.com/item/32903378127.html on each en

I think this is interesting BUT it uses "I2C". That is a way of talking that requires too much programming.

Another bad idea.
This IC is used as a meter in audio amplifiers. There are 10 put puts. In DOT mode only one LED is on and in BAR mode all LEDs below the level are on. So it reads 10 voltage levels and indicates which level is right. There are two versions. (linear and log)
I removed the input diodes and caps and added a 10k pull up resistor. The switches pull down with a different resistor for each. If S1 has a 10k resistor it will pull down to 1/2 supply. S2 and S3 will have different values and cause a different output to turn on. This IC can act like a 5 LED driver by shorting pin1-18, pin 17 to 16 etc.

I can not find it now but there is a simple 4 or 5LED version some where.
So on the remote end there are 4 switches and 3 or 4 resistors. On the PCM end, it will look at 4 of the outputs.
If this looks good I can look more for the simple IC that is some thing like this one.

 

[ronsimpson]

Found the IC: LB1413

If the 10k VR is set to the top then when IN approaches 0.33 volts pin-1 goes low. At about 0.67V then pin 2 goes also low. By 1.67V pin 6 drops.
If you want twice that voltage adjust VR to the 1/2 point.
Probably should have a 0.1uF cap from pin-8 to ground to help remove noise.
I have not tried this circuit. I do not know exactly how low pin 1-6 will go or how high. I think 0.5V to 5.0V. This needs to be tested.

I forgot to add a 10k resistor from IN to VCC. The switches and resistors are not shown.

 

[sellis]

Thanks everyone. Definitely gives me some direction. I will do some experimenting and see what works best.