Considerable voltage drop at MUX o/p while connecting mux

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arup

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Dear sir,

Kindly help for following problem :

I am reading dc voltage at on-chip adc i/p of PIC 18F6585 microcontroller thro MUX (part no : HEF4067).But Observed considerable voltage drop at MUX o/p.Hence adc reading corrupted.

MUX VCC : 5V
Micro VCC : 5V
DC voltage(i/p to LM324 based ckt) : 2 - 15 V


What could be the reason?
What would be the steps to troubleshoot this problem ??


Reagards,

Arup
 

Did you read the datasheet? Philips page 2

The analogue inputs/outputs (Y0 to Y15 and Z) can swing
between VDD as a positive limit and VSS as a negative
limit.
 

Re: Considerable voltage drop at MUX o/p while connecting mu

Hi,
The Mux can not handle analog voltage more than its Vcc. Same may be true of the Microcontroller also. What is the analog level at the output of LM324?, which I think is connected to the Mux. Please check these aspects and post a schematic of the input circuit to ADC, if still problem persists.
Regards,
Laktronics
 

Re: Considerable voltage drop at MUX o/p while connecting mu

Thanks All!,

The analog i/p to MUX is within limit i.e within VCC of MUX and Micro.
The problem is in firmware.Port pin is not configured properly.It was first configured as i/p and then it was changing as o/p .
Now it's solved and micro is not loading.

thanks,

Arup
 

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