How to amplify the current from Voltage divider?

[Screech]

The current coming out of my 600kilo-ohms voltage divider is vary low.
This voltage is to be read by a microcontroller(picaxe)
The problem is that the microcontroller can only read voltages with 10k impedience with accuracy.
So,I nead to increase the current, but not the voltage.

Beaniebots told me Op-amps can do this.
I didn't think they amplify current.

Do they amplify voltage and curent, and then do I run another voltage divider after the Op-Amp? (I know nothing about OP-Amps)



I must use the primary 600k divider network!
Thanks

 

[Nigel Goodwin]

The current coming out of my 600k voltage divider is vary low.
This voltage is to be read by a microcontroller(picaxe)
The problem is that the microcontroller can only read voltages with 10k impedience with accuracy.
So,I nead to increase the current, but not the voltage.

Beaniebots told me Op-amps can do this.
I didn't think they amplify current.

Do they amplify voltage and curent, and then do I run another voltage divider after the Op-Amp? (I know nothing about OP-Amps)

Yes, they amplify both, you just need a unity gain (voltage gain!) buffer, pick an opamp with high impedance inputs, a jfet based one should be fine (TL072 series).

 

[Screech]

Yeah, my supplyer sells that 8 pin dual low noise JFET op-amp (type TL072/LF353)

Thanks ,Nigel.

I'm off to study up on op-omps

 

[Screech]

so, its a voltage follower I need?


Here's what I found:

Voltage Follower:

The voltage follower, also called a buffer, provides a high input impedance, a low output impedance, and unity gain. As the input voltage changes, the output and inverting input will change by an equal amount.
__________________________________________________________


Do I wire it up exactly as the pic on the bottom right.
It neads +5 and -5 volts supply to it, yeah?

Thanks

 

[Nigel Goodwin]

so, its a voltage follower I need?


Here's what I found:

Voltage Follower:

The voltage follower, also called a buffer, provides a high input impedance, a low output impedance, and unity gain. As the input voltage changes, the output and inverting input will change by an equal amount.
__________________________________________________________


Do I wire it up exactly as the pic on the bottom right.
It neads +5 and -5 volts supply to it, yeah?

Yes, it's the bottom right diagram, and I would recommend that you use a +/- supply. One problem you may have is that the opamp may not go fully to +5V, even a rail to rail opamp may not be 100%.

If you check my analogue PIC tutorial you will see that I use an external 2.5V reference, so the opamp only has to output between 0V and 2.5V, this prevents any potential problems! - it also makes the conversion more accurate and repeatable.

 

[Screech]

Fantastic.
Thanks again mate.

 

[Screech]

Nigel said

If you check my analogue PIC tutorial you will see that I use an external 2.5V reference, so the opamp only has to output between 0V and 2.5V, this prevents any potential problems! - it also makes the conversion more accurate and repeatable.

I saw your tutorial.
but, are you saying you are using the 2.5 volt reference as the possitive supply?
What about the minus supply?
:shock:

 

[Nigel Goodwin]

Nigel said

If you check my analogue PIC tutorial you will see that I use an external 2.5V reference, so the opamp only has to output between 0V and 2.5V, this prevents any potential problems! - it also makes the conversion more accurate and repeatable.

I saw your tutorial.
but, are you saying you are using the 2.5 volt reference as the possitive supply?
What about the minus supply?
:shock:

No, I'm saying use +/-5V supplies, but use a 2.5V reference on the PIC, this way the PIC input is from 0-2.5V, rather than 0-5V, which is well within the range of almost any opamp.

 

[Screech]

Nigel said

No, I'm saying use +/-5V supplies, but use a 2.5V reference on the PIC, this way the PIC input is from 0-2.5V, rather than 0-5V, which is well within the range of almost any opamp.

I see.
But, A.F.A.I.K. the picaxe programmer will not allow 0-2.5v reference.
There is no command for this feature with the Picaxe's basic laungage code.
Can only use the Picaxe's supply voltage as the reference supply.

Thanks again Nigel.
I'm off to get that op-amp.