Reply by jmariano ●September 30, 20202020-09-30
On Sunday, 27 September 2020 at 07:03:39 UTC+1, ehsjr wrote:

> On 9/25/2020 4:19 PM, jmariano wrote: 
> > Dear All, 
> > 
> > Does anyone have any experience in using one of this digital pot from this Microchip family? 
> > 
> > My project requires that I control a voltage divider from the computer, so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm able to control it, no problem, thanks to Greg Srabian's library. I can program the wiper position and see the resulting resistance changing on my ohmmeter. 
> > 
> > What I can't figure out, from reading the datasheet, is how to connect the analog side power pins and to those to the potentiometer (eventually). 
> > 
> > So, my voltage divider must be between GND and -10V. I have available on my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to -10; one side of the potentiometer to GND; the other to -10V. 
> > Is this correct? 
> > I would be more comfortable if could just apply 0 and -10V to the end terminals of the potentiometer and power the analog part of the chip from the +13V ps, but i'm not sure this would work.... 
> > 
> > I guess what is unclear to me is the relation (if any) between the voltage on the V+ and V- pins and the voltage at the potentiometer end terminals. 
> > 
> > Any suggestions would be very welcomed, thank you very much! 
> > 
> > Regards 
> > jmariano 
> >
> Wire the potentiometer pins like you would any 
> potentiometer. So, you have it right: one side 
> of the pot to GND, the other to -10. The output 
> of the divider is the wiper pin of the pot. 
> 
> Be aware that this is a low current potentiometer. 
> 
> Ed


Good evening,

I took Phil's advice and read the data sheet carefully, again. Oh, boy, those things are hard to read, or maybe my English is not that good, but it seams that everything is there except what you are looking for...  Anyway, is not easy to figure out how the chip works, because not many details are given about the inner structure of the chip, but from what I as able to understand, the voltage difference between the potentiometer terminals A and B, what they call the Resistor Network Supply Voltage, must be between V- and V+. 
Tomorrow I will give it a try.
Thank you Phil and Ed for taking the time to help me.
Regards
jmariano
Reply by ehsjr ●September 27, 20202020-09-27
On 9/25/2020 4:19 PM, jmariano wrote:

> Dear All,
> 
> Does anyone have any experience in using one of this digital pot from this Microchip family?
> 
> My project requires that I control a voltage divider from the computer, so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm able to control it, no problem, thanks to Greg Srabian's library. I can program the wiper position and see the resulting resistance changing on my ohmmeter.
> 
> What I can't figure out, from reading the datasheet, is how to connect the analog side power pins and to those to the potentiometer (eventually).
> 
> So, my voltage divider must be between GND and -10V. I have available on my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to -10; one side of the potentiometer to GND; the other to -10V.
> Is this correct?
> I would be more comfortable if could just apply 0 and -10V to the end terminals of the potentiometer and power the analog part of the chip from the +13V ps, but i'm not sure this would work....
> 
> I guess what is unclear to me is the relation (if any) between the voltage on the V+ and V- pins and the voltage at the potentiometer end terminals.
> 
> Any suggestions would be very welcomed, thank you very much!
> 
> Regards
> jmariano
> 


Wire the potentiometer pins like you would any
potentiometer.  So, you have it right: one side
of the pot to GND, the other to -10. The output
of the divider is the wiper pin of the pot.

Be aware that this is a low current potentiometer.

Ed
Reply by Phil Hobbs ●September 25, 20202020-09-25
On 2020-09-25 18:22, jmariano wrote:

> On Friday, 25 September 2020 at 21:35:27 UTC+1, Phil Hobbs wrote:
>> On 2020-09-25 16:19, jmariano wrote:
>>> Dear All,
>>>
>>> Does anyone have any experience in using one of this digital pot from this Microchip family?
>>>
>>> My project requires that I control a voltage divider from the computer, so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm able to control it, no problem, thanks to Greg Srabian's library. I can program the wiper position and see the resulting resistance changing on my ohmmeter..
>>>
>>> What I can't figure out, from reading the datasheet, is how to connect the analog side power pins and to those to the potentiometer (eventually).
>>>
>>> So, my voltage divider must be between GND and -10V. I have available on my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to -10; one side of the potentiometer to GND; the other to -10V.
>>> Is this correct?
>>> I would be more comfortable if could just apply 0 and -10V to the end terminals of the potentiometer and power the analog part of the chip from the +13V ps, but i'm not sure this would work....
>>>
>>> I guess what is unclear to me is the relation (if any) between the voltage on the V+ and V- pins and the voltage at the potentiometer end terminals.
>>>
>>> Any suggestions would be very welcomed, thank you very much!
>> The logic supply VL and the ground pin have to be between V+ and V-, so
>> if you ground V+ and VL you'll have to make another rail for the ground
>> pin, and you'll have to level-shift the SPI.
>>
>> That's not that hard to do, but with a 36V part there's no reason to.
>>
>> I'd use
>>
>> V+ -> +13
>> VL -> +5
>> GND -> 0V
>> V- -> -10
>>
>> You can also use +5 for V+, but I suspect it's probably a noisier rail.



> 
> Hello Phil,
> 
> Thanks for your help, understood!
> I don't want to push my luck, but how about the relation between the voltages at the potentiometer ends (P0A and P0B) and V+ and V-? P0A and P0B must also be between V+ and V-?
> That means that for my purposes I can use
>   V+ -> +13
>   VL -> +5
>   GND -> 0V -> P0A
>   V- -> -10 -> P0B
> Is that it?


How did you reach that conclusion? (I'm not saying it's wrong or right 
here.)

I suggest reading the datasheet carefully yourself, and thinking about 
how the chips actually work.  That's a bit harder these days because 
datasheets have become marketing documents rather than engineering ones, 
but there are certain regularities that you'll learn as you go along.

There are chips that work fine with their inputs way outside the supply 
rails, but they're rare.

Old ones, such as the LM324/358/339 family, often have useful properties 
accidentally.  Those ones have lateral PNP input transistors without 
protection diodes, so they'll survive having their inputs pulled as high 
as 35V from the negative supply even if the positive supply is much 
lower. (Of course if both inputs are outside the positive common mode 
limit the chip doesn't work properly, but it doesn't die.)

For newer ones they usually trumpet such things, e.g 'Beyond The Rails' 
op amps.

Cheers

Phil Hobbs



Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
Reply by jmariano ●September 25, 20202020-09-25
On Friday, 25 September 2020 at 21:35:27 UTC+1, Phil Hobbs wrote:

> On 2020-09-25 16:19, jmariano wrote: 
> > Dear All, 
> > 
> > Does anyone have any experience in using one of this digital pot from this Microchip family? 
> >
> > My project requires that I control a voltage divider from the computer, so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm able to control it, no problem, thanks to Greg Srabian's library. I can program the wiper position and see the resulting resistance changing on my ohmmeter..
> > 
> > What I can't figure out, from reading the datasheet, is how to connect the analog side power pins and to those to the potentiometer (eventually). 
> > 
> > So, my voltage divider must be between GND and -10V. I have available on my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to -10; one side of the potentiometer to GND; the other to -10V. 
> > Is this correct? 
> > I would be more comfortable if could just apply 0 and -10V to the end terminals of the potentiometer and power the analog part of the chip from the +13V ps, but i'm not sure this would work.... 
> > 
> > I guess what is unclear to me is the relation (if any) between the voltage on the V+ and V- pins and the voltage at the potentiometer end terminals. 
> > 
> > Any suggestions would be very welcomed, thank you very much!
> The logic supply VL and the ground pin have to be between V+ and V-, so 
> if you ground V+ and VL you'll have to make another rail for the ground 
> pin, and you'll have to level-shift the SPI. 
> 
> That's not that hard to do, but with a 36V part there's no reason to. 
> 
> I'd use 
> 
> V+ -> +13 
> VL -> +5 
> GND -> 0V 
> V- -> -10 
> 
> You can also use +5 for V+, but I suspect it's probably a noisier rail. 
> 
> Cheers 
> 
> Phil Hobbs 
> 
> -- 
> Dr Philip C D Hobbs 
> Principal Consultant 
> ElectroOptical Innovations LLC / Hobbs ElectroOptics 
> Optics, Electro-optics, Photonics, Analog Electronics 
> Briarcliff Manor NY 10510 
> 
> http://electrooptical.net 
> http://hobbs-eo.com


Hello Phil,

Thanks for your help, understood! 
I don't want to push my luck, but how about the relation between the voltages at the potentiometer ends (P0A and P0B) and V+ and V-? P0A and P0B must also be between V+ and V-? 
That means that for my purposes I can use
 V+ -> +13 
 VL -> +5 
 GND -> 0V -> P0A 
 V- -> -10 -> P0B
Is that it?

Regards

jmariano
Reply by Phil Hobbs ●September 25, 20202020-09-25
On 2020-09-25 16:19, jmariano wrote:

> Dear All,
> 
> Does anyone have any experience in using one of this digital pot from this Microchip family?
> 
> My project requires that I control a voltage divider from the computer, so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm able to control it, no problem, thanks to Greg Srabian's library. I can program the wiper position and see the resulting resistance changing on my ohmmeter..
> 
> What I can't figure out, from reading the datasheet, is how to connect the analog side power pins and to those to the potentiometer (eventually).
> 
> So, my voltage divider must be between GND and -10V. I have available on my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to -10; one side of the potentiometer to GND; the other to -10V.
> Is this correct?
> I would be more comfortable if could just apply 0 and -10V to the end terminals of the potentiometer and power the analog part of the chip from the +13V ps, but i'm not sure this would work....
> 
> I guess what is unclear to me is the relation (if any) between the voltage on the V+ and V- pins and the voltage at the potentiometer end terminals.
> 
> Any suggestions would be very welcomed, thank you very much!


The logic supply VL and the ground pin have to be between V+ and V-, so 
if you ground V+ and VL you'll have to make another rail for the ground 
pin, and you'll have to level-shift the SPI.

That's not that hard to do, but with a 36V part there's no reason to.

I'd use

V+ -> +13
VL  -> +5
GND -> 0V
V- -> -10

You can also use +5 for V+, but I suspect it's probably a noisier rail.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
Reply by jmariano ●September 25, 20202020-09-25
Dear All,

Does anyone have any experience in using one of this digital pot from this Microchip family? 

My project requires that I control a voltage divider from the computer, so i'm using an Arduino to control an MCP41HV51 digital pot via SPI. I'm able to control it, no problem, thanks to Greg Srabian's library. I can program the wiper position and see the resulting resistance changing on my ohmmeter. 

What I can't figure out, from reading the datasheet, is how to connect the analog side power pins and to those to the potentiometer (eventually).  

So, my voltage divider must be between GND and -10V. I have available on my system +13V, +5V and -10V. I was thinking to connect V+ to GND; V- to -10; one side of the potentiometer to GND; the other to -10V. 
Is this correct?  
I would be more comfortable if could just apply 0 and -10V to the end terminals of the potentiometer and power the analog part of the chip from the +13V ps, but i'm not sure this would work....

I guess what is unclear to me is the relation (if any) between the voltage on the V+ and V- pins and the voltage at the potentiometer end terminals.

Any suggestions would be very welcomed, thank you very much!

Regards
jmariano