My Schematic and Your Recommendations

[musti463]

Can you tell me your recommendations about my schematic?

https://yadi.sk/i/yB38eXkXbapCH
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M.Emir SADE

[dyeatman]

OK, so you show a schematic.
What do you want to know.
What is it supposed to do?
Where is your CCS code?
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[temtronic]

I could make about 40-50 'recommendations' though this is not the forum for that rather dedicated programming of PICs using CCS C.


A schematic is just one piece of the puzzle to get a product to market. You also need GREAT board layout(easy these days) as well as very good code(super easy with CCS C !).


hth
jay

[SherpaDoug]

Hard to say much without knowing a lot about the application, but be careful how you lay out your grounds.
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[musti463]

Yes, i know there is no ccs code. But i wanna create firstly hardware correctly and later create a ccs code. I want your help for my circuit schematic, later i share my layout and lastly my ccs code.

This circuit will suitable. So there are many inputs i know. There are totally 4 sensor inputs but sometimes output types can change 4/0,3/1,/2/2,1/3(mA/V) etc. And my MCU generates some values and send to operator panel circuit and display this values on GLCD. And so while values at critical. System control the crane movements with relays outputs.
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M.Emir SADE

[asmboy]

Differential inputs for single ended sources are delusional and a waste of parts.

this will NOT fix offsets and NOT reject common mode
( as its all common mode when unbalanced !!) BUT
WILL increase the noise floor up to 3db
in the output signal for U1 -

you would be better off with a simple
BUFFER with ONLY the 100 ohm input "bias/load/terminator left .
just tie the inverting input to the op amp output and buffer

better yet get rid of U1A as you already have a 100 ohm term resistor into the SK filter stage that follows

this design does not need U1A at all so long as there is that 100 ohm resistor present!!

a quick look says the SK follower may be only conditionally stable too !!!

you need some analog chops - don't just cut and paste circuit elements!!!
thats my advice

[musti463]

thank you asmboy. You mean "remove all U1:A,U2:A,U3:A.... circuits" ?. To be honest i get this circuit from an industrial device
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M.Emir SADE

[asmboy]

YUP!!
just keep the 100 ohm resistor

[temtronic]

I'd put LEDs in both sides of the opto-couplers of the 'relay outputs'. I've done this for 2 decades in my SSRs and it's saved a LOT of 2Am calls for 'no heat' ! A simple look at the board shows IF the LED is on the relay is working, so 'no heat ' problem is NOT my board must be your furnace.

As for PCB layout, bigger is better. I'd use a 4" x 6" (my standard) PCB, with fat traces for power and grounds. I prefer a checkerboard ground plane not a 'fill', especially if the 2 board surfaces greatly differ in copper. More on one side will 'cup' the PCB. Always use sockets for PIC, never run traces between adjoining pins if possible.

Why socket the PIC? 3 days after the PCB is done, you'll need more RAM, or EEPROM or the new PIC will be 1/2 the cost !

hth
jay

[gpsmikey]

While I agree with the idea of a socket for the PIC, you need to consider if it is going to be used in a high humidity or vibration environment. Both of those can make a socket more trouble than it is worth.

mikey
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mikey
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[ckielstra]

[dyeatman]

Isn't redesigning a commercial circuit just a bit far afield for this board?
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[PCM programmer]

It's getting off topic. It really should be done on a hardware forum.
This one,
http://www.edaboard.com
or maybe this one:
http://forum.allaboutcircuits.com

[temtronic]

ck is right about using a different PIC with a better ADC built in.It allows for as good(if not better performance),cheaper overall, easier to code,etc.

As for sockets, I've used gold plated ones and a dab of low tack sealant in industrial boards(in foundries,paint shops,etc.) for ,ugh, 2 decades(originally 16C84s) and have never had any problems related to socket-itis.

jay

[musti463]

thanks for your advices. There is easy to use MCP3208 with PIC. Because there is MCP3208.c in CCS C Library right?

1-So how is 18F46K80 (internal 12bit ADC). And so there isn't AVSS pin on 18F46K80. How can i provide the good ADC performance?

2-Can ADC performance be different PIC to PIC ?

@PCM Programmer i asked same question at edaboard.com. But i found better answers and better attention here!
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M.Emir SADE