whats negative voltage?

[flightline]

Dear Sirs:

I am replacing a 5K rotary linear pot with a digital pot (DS1804) and controller (basic stamp). I will from my computer then be able to control a pot which in turn controls an amplifier's output.

My first problem is I do not understand the difference between negative voltage and ground. The 5K pot is connected to +8v, -8v and the wiper to an input on an amplifier according to schematics. But the digital pot is looking for +6V, a ground (not negative voltage) and input. I must also somehow lower the voltage from 8V to 6V so as not to burn the digital pot and figure out how to ground it. Does anyone have the patients to help me on this one? Thank you very much.

 

[elec_lover]

1/ If you take 2 batteries of 9 volt and connect the plus from one battery to the minus from the other. You have now 18 Volt on the not connected contacts.
But if you take the middle as a reference point, then you have +9 Volt
on the battery where the - is connected to the + of the other battery (common point), and -9volt where the + is connected to the common point. It is easy to understand, because the - and + signs are on the battery.
Thats why you have a negative voltage compared to the reference point.
Similar you can build a dual powersupply with a common point called
ground.

         -   < -battery+ > < -battery+ >  +    = 18 Volt power supply

or       - 9 Volt       ground       + 9 Volt

2/ DS1804

From the DS1804 datasheet:

H - High-Terminal Potentiometer. This is the high terminal of the potentiometer. It is not required that
this terminal be connected to a potential greater than the L-terminal. Voltage applied to the H-terminal
can not exceed the power-supply voltage, VCC, or go below ground.
L - Low-Terminal Potentiometer. This is the low terminal of the potentiometer. It is not required that this
terminal be connected to a potential less than the H-terminal. Voltage applied to the L-terminal cannot
exceed the power-supply voltage, VCC, or go below ground.

So this digital pot DS1804 CAN NOT BE USED in your application.
( on -8 Volt and + 8 Volt )

 

[ljcox]

What elec_lover said is correct.

In his example, the "ground" ie. the mid point between the 2 batteries, is 0 Volt. Thus if you connect a voltmeter to ground, you will measure +9 Volt at the positive terminal of one battery and -9 Volt at the negative terminal of the other and 0 Volt at the mid point.

Incidentally, you meant to type patience, not patients

Len

 

[flightline]

thank you gentlemen

I am now a little less dumb.

Elec_lover is there anyway to use any circuit that could employ a digital pot with only +8,-8V and wiper output??

 

[etrc]

Dear Sirs:

I am replacing a 5K rotary linear pot with a digital pot (DS1804) and controller (basic stamp). I will from my computer then be able to control a pot which in turn controls an amplifier's output.

My first problem is I do not understand the difference between negative voltage and ground. The 5K pot is connected to +8v, -8v and the wiper to an input on an amplifier according to schematics. But the digital pot is looking for +6V, a ground (not negative voltage) and input. I must also somehow lower the voltage from 8V to 6V so as not to burn the digital pot and figure out how to ground it. Does anyone have the patients to help me on this one? Thank you very much.

 

[ljcox]

Re: thank you gentlemen

I am now a little less dumb.

Elec_lover is there anyway to use any circuit that could employ a digital pot with only +8,-8V and wiper output??

You are not dumb, just learning. It is a bit difficult to assist without a circuit to look at. So if you can post the relevant part of your circuit and the data sheet of the digital pot, we should be able to help you.

Len