4 - 20 mA meter possible?

[aljamri]

As Instrumentation Tech, we had a lot of repeated problems. One of them is lossing the panel meters and not getting replacement simillar in size and specifications, so that i thought if possible to make a panel meter using my new world of PIC using Assemblly and PIC16F876 with the following Specs:

4 - wire meter ( not loop supplied )
4 - 20 mA input ( or 1 to 5 V using 250hm: Resistor )
0 - 10 output figures using two units of 7-Sigments LED ( Common Cathode ) with reselution of 0.1
if it is possible and got a room from the outputs we may need two alarming set points for LO and HI signalling.

All replys are very wellcommed starting from YES or NO and not ending with Web Links and Schematics. If it is possible i'll set this my next goal to achive.

Thanks

 

[Leftyretro]

As Instrumentation Tech, we had a lot of repeated problems. One of them is lossing the panel meters and not getting replacement simillar in size and specifications, so that i thought if possible to make a panel meter using my new world of PIC using Assemblly and PIC16F876 with the following Specs:

4 - wire meter ( not loop supplied )
4 - 20 mA input ( or 1 to 5 V using 250hm: Resistor )
0 - 10 output figures using two units of 7-Sigments LED ( Common Cathode ) with reselution of 0.1
if it is possible and got a room from the outputs we may need two alarming set points for LO and HI signalling.

All replys are very wellcommed starting from YES or NO and not ending with Web Links and Schematics. If it is possible i'll set this my next goal to achive.

Thanks

Well it is all possible, none of your requirements are hard to reach with a PIC, however your third requirment would require three 7 segment decimal displays in that you specified .1% resolution which will requires a 0-999 display capacity, displaying as XX.X%.


Good luck
Lefty

 

[aljamri]

Well it is all possible, none of your requirements are hard to reach with a PIC, however your third requirment would require three 7 segment decimal displays in that you specified .1% resolution which will requires a 0-999 display capacity, displaying as XX.X%.

Lefty

This remided me of another Spec. if possible which will save one 7-Seg and will not require a minus sign.

we may add two LED's to show if the Input below 4mA ( 1V ) and over 20mA ( 5V ). This situation is likely to happen in our area of industry.

 

[aljamri]

i am reading Nigel's analog tutorial to get idea how to start. but is 16F876a has enough pin for all my requirments:

analog input ( voltage or current )
output to TWO 7-segments
two alarm set points indications
two over/under range indications

 

[Hank Fletcher]

i am reading Nigel's analog tutorial to get idea how to start. but is 16F876a has enough pin for all my requirments

I think you'd be pushing the limits, but that depends on how you plan to drive the LED display. If you used BCD to 7-segment drivers (like the 74LS47) instead of driving the LED display directly from the PIC, you'd save considerably on the amount of PIC output pins you'd need (four or five for each LED digit as oppose to seven or eight, depending on whether you're using a decimal point).

I don't fully understand your plan for these:

two alarm set points indications
two over/under range indications

but depending on what they are and what you need, you might be able to accomplish what you want even without using the BCD to 7-segment drivers. Sorry I can't be of more help, but it doesn't seem like your PIC's datasheet is on the Microchip website - I just get diverted to the 16F877. I don't know how different that is from what you have, so it's hard for me to say. It seems that with the amount of I/O pins your PIC has (22, right?), that what you want should be possible, depending on what you need for your alarm set points and outside-range indications.

 

[aljamri]

I don't fully understand your plan for these:

i need just single LED for each alarm set point to be let when certain limit reaches say 25% for LO and 85% for Hi ( preset in program )

Sorry I can't be of more help, but it doesn't seem like your PIC's datasheet is on the Microchip website - I just get diverted to the 16F877.

You are right they are at the same data sheet PIC16F87X along with another one. but my chip is 28pins. 16F877 is 40 pins.

 

[Nigel Goodwin]

i am reading Nigel's analog tutorial to get idea how to start. but is 16F876a has enough pin for all my requirments:

analog input ( voltage or current )
output to TWO 7-segments
two alarm set points indications
two over/under range indications

Plenty of I/O pins on a 16F876 for you!, even a 16F88 or 16F819 would have enough.