Cheap part useable as a vref 0.7 - 3v - Electronic Circuits Projects Diagrams Free

William At MyBlueRoom · 4th July 2006, 04:54 PM

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?

**Nigel Goodwin** · 4th July 2006, 05:14 PM

Quote:

Originally Posted by William At MyBlueRoom

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?

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.

William At MyBlueRoom · 4th July 2006, 05:33 PM

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.

akg · 5th July 2006, 08:13 AM

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

William At MyBlueRoom · 5th July 2006, 05:48 PM

Quote:

Originally Posted by akg

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

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

**Nigel Goodwin** · 5th July 2006, 07:58 PM

Quote:

Originally Posted by William At MyBlueRoom

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

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.

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4th July 2006, 04:54 PM	(permalink)
William At MyBlueRoom	Cheap part useable as a vref 0.7 - 3v 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? __________________ Bill Home of the Firefly PIC Tutor Inchworm ICD2 http://www.blueroomelectronics.com

5th July 2006, 08:13 AM	(permalink)
akg	If u need precise 0.7V , use a resistive voltage divider with the 2V5 source __________________ Gods own Country Incredible !ndia www.flickr.com/photos/_akg/ "Give a man a fish, and he will eat for a day. Teach that man to fish, and he will eat for a lifetime."