#1 2015-05-02 13:34:54

Stanley
Member
From: Kuala Lumpur, Malaysia
Registered: 2014-12-01
Posts: 65
Website

Simple MCP602 op amp before Analog0 pin

To increases the packet decoding, I added a simple op amp ( MCP602 ) before the Analog0 pin..

16719666634_9e1605caa2_m.jpg by stanley_seow

It was working fine and all of the sudden, it does not work anymore...

The input is 5V going thru a 1N4001 diode to drop the voltage 5V ( not shown in the diagram ) to give 4.4V Vcc

I'm using 2 x 10K to Vcc & Gnd to the non-inverting input , give around 2.2V

I had to touch the inverting input ( - ) and only the op amp works...

I measured voltage on ( - ) and ( + ) pins and they are near to Zero ( op amp seems to be working ) ....


Can someone help to explain why this happens ??

Is the circuit correct ? ( I'm very new to op amp )

How to fix this issue / circuit ?

Screenshot on the oscilloscope :-

17134739357_945f1c534d_m.jpgMCP602 op amp not working by stanley_seow, on Flickr


16721928003_91b4f04363_m.jpgMCP602 working when finger touch the inverting input pins by stanley_seow, on Flickr


Stanley
9W2SVT/ N5SVT
http://9W2SVT.blogspot.com

Offline

#2 2015-05-03 10:48:55

G4ZAL
Member
Registered: 2015-04-28
Posts: 14

Re: Simple MCP602 op amp before Analog0 pin

Here is a circuit I have seen for the same op-amp and APRS
https://michaldemin.files.wordpress.com … etter1.png

Complete article
https://michaldemin.wordpress.com/2012/ … -afsk-tnc/

HTH

Nigel.

Offline

#3 2015-05-04 07:18:25

Stanley
Member
From: Kuala Lumpur, Malaysia
Registered: 2014-12-01
Posts: 65
Website

Re: Simple MCP602 op amp before Analog0 pin

Dear Nigel,

Thanks for the links ...

I somehow swapped the input 100nF cap and 1K resistor and it seems to work... ( still no idea why it happens ) ....

I followed this site to do a high pass filter to only allow 1000Hz freq to pass-thru ... ( high pass filter still not working yet )
http://www.ekswai.com/en_highpass.htm


Stanley
9W2SVT/ N5SVT
http://9W2SVT.blogspot.com

Offline

Board footer

Powered by FluxBB