Cheap part useable as a vref 0.7 - 3v

William At MyBlueRoom said:

What cheap part (like a zener) would be useable as a vref
between 0.7v & 3v

1n4148 = 0.7 is it accurate?

It's for an A/D pin on a PIC.

Ideas?

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Use a TL431 as in my tutorials, this is a precision 2.5V adjustable reference IC, 2.5V is it's minimum. You don't want to use 0.7V. it's too low.

Found it, nice. Just 2.2K and tie two pins together is 2.5v?

PS I love Abacom products. I use the PCB layout software, might look at their capture software too. I wonder is Splan can be used for protoboards?

PS thanks Nigel, these forums are very helpful. Great job to you and the other admins.

If u need precise 0.7V , use a resistive voltage divider with the 2V5 source

akg said:

If u need precise 0.7V , use a resistive voltage divider with the 2V5 source

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Just wanted a voltage below 3V that could be used as a vref on a PIC with a variable VDD.

William At MyBlueRoom said:

Just wanted a voltage below 3V that could be used as a vref on a PIC with a variable VDD.

Click to expand...

If you examine my tutorial hardware, you will see the reasoning behind using a 2.5V reference:

1) It's a precision reference.

2) It's easily and cheaply available (and you can find them for free in many old TV's and VCR's).

3) Because it's 2.5V the opamp feeding the A2D doesn't need to go to the positive rail.

4) By using a 7660 to give an extra -ve rail, it doesn't have a problem going to exactly zero volts either.