moose4621:
I have put this capacitor between V+ and GND on the 7660. Is this also sufficient for the TL082 as this line also goes to it's power pin?
No. Every digital chip needs its own decoupling. Analog chips such as the opamp don't: they need the power supply to be stabilised with large caps.
Note the DC:DC converter is a special case of digital chip and it should have whatever caps the datasheet calls for.
If you have a 12V AC plugpack then generating the required negative rail is simple.
MorganS:
No. Every digital chip needs its own decoupling. Analog chips such as the opamp don't: they need the power supply to be stabilised with large caps.Note the DC:DC converter is a special case of digital chip and it should have whatever caps the datasheet calls for.
If you have a 12V AC plugpack then generating the required negative rail is simple.
OK, so remove C9 and run dc:dc converter IAW data sheet.
Now for the OPAMP. The original circuit I am copying has no caps on the power supply. Should I add them or run as per original circuit do you think?
TomGeorge:
Hi,
If you are copying this.Check your +12V and -12V supplies.
Thanks Tom, good catch. I am a numpty for missing that!
Many thanks to those with infinite wisdom who have given me their time on this project.
Revision 4 of schematic.
Hi,
Nope.
You still have the cathode of D3 and D6 going to V+, in the original the equivalent goes to V-.
You still have the cathode of D1 and D4 going to V-, in the original the equivalent goes to V+.
Thats what the RED labels were indicating. And I said" Check your +12V and -12V supplies."
Tom... 
Now I'm an even bigger numpty!!
Thanks Tom.
I went all "artistic" this time and colour coded everything to make it easier to follow.
Schematic R5.
OK, 9 downloads and no comments yet. "No news is good news"?
So on to the PCB layout.
Is "ground fill" appropriate for this circuit?
If you have a ground plane, you don't need ground traces.
The parts placement looks a little haphazard, you can arrange them to make things look neater and the trace routing straighter.
CrossRoads:
If you have a ground plane, you don't need ground traces.
The parts placement looks a little haphazard, you can arrange them to make things look neater and the trace routing straighter.
Thanks very much for your advice CrossRoads.
I left the ground traces in there to help me visualize the circuit as the ground fill is done last. I am using the "toner transfer" method so the final copper mask looks the same anyway.
As for the parts placement, I agree with you completely and I get frustrated when placing components as it always come out looking like a dog's dinner. There must be a method or procedure to getting neat layouts and I obviously have no idea what it is.
There must be a method or procedure to getting neat layouts and I obviously have no idea what it is.
Practice.
Grumpy_Mike:
Practice.
Ha ha, great. Thanks:)
Only minor improvements I know but ...... 
Thanks again to everyone for their help. Very much appreciated and saved me a lot of frustration.
If anyone is interested in making this, I have attached the files for toner transfer.
Might be a bit premature since I haven't made one yet but at least it is of a known design.
My opinion of F**ing is dropping.
No the colours don't help understanding the schematic. If you highlight one net of interest to ask a question it might be useful. What would really help would be ground symbols. That will strip a lot of unnecessary lines out of it.
What frequencies are you putting into this? If there are any components above audio frequencies (or sharp-edged digital pulses) then you are going to get crazy reflections off all those strange corners on the PCB traces. Try to make all turns 45 degrees.
The output wires crossing over the entire board will either pick up interference or give interference to the input stage. If you can't use a 2-sided board then make this a flying lead for the whole distance. If high frequency then make it shielded coax.
I can't believe that 10nF is all the capacitance required. I would put much bigger caps on both 12V rails. Like 1000 times bigger.
Try to place your parts in consistent rows. Group as many resistors together as possible. The traces underneath can get complex but this complexity is free. Hand placement of parts is expensive, particularly when you have many identical-looking parts with different values. Put all the 1k resistors together and adjust the values of non-critical resistors so they are the same values.
Then you need to add some input and output protection. Can the probes accidentally touch 110V? You can't make your circuit immune to all possible faults but at least you can prevent damage to downstream components.
HAI
** ADD IN A DETERMISTICALLY GROUND /// MID POINT OF ZERO VOLTS UNLESS YOU POWER SUPPLY ALREADY HAS +12>0>-12 THEN YOU CANNOT BE WRONG
BYE FOR NOW _ D
Thanks for your time MorganS, Much appreciated.
MorganS:
My opinion of F**ing is dropping.No the colours don't help understanding the schematic. If you highlight one net of interest to ask a question it might be useful.
Well, what can I say? Sorry? The colours certainly help me identify parts of the circuit.
MorganS:
What would really help would be ground symbols. That will strip a lot of unnecessary lines out of it.
Agreed. Doesn't seem to be an option in Fritzing though.
MorganS:
What frequencies are you putting into this? If there are any components above audio frequencies (or sharp-edged digital pulses) then you are going to get crazy reflections off all those strange corners on the PCB traces. Try to make all turns 45 degrees.The output wires crossing over the entire board will either pick up interference or give interference to the input stage. If you can't use a 2-sided board then make this a flying lead for the whole distance. If high frequency then make it shielded coax.
I can't believe that 10nF is all the capacitance required. I would put much bigger caps on both 12V rails. Like 1000 times bigger.
I guess you need to read the links in post #1 for the answers to those questions and comments.
MorganS:
Try to place your parts in consistent rows. Group as many resistors together as possible. The traces underneath can get complex but this complexity is free. Hand placement of parts is expensive, particularly when you have many identical-looking parts with different values. Put all the 1k resistors together and adjust the values of non-critical resistors so they are the same values.
I take your point. My layout certainly isn't pretty. I seem to finish up with too many jumpers if try "complex".
MorganS:
Then you need to add some input and output protection. Can the probes accidentally touch 110V? You can't make your circuit immune to all possible faults but at least you can prevent damage to downstream components.
Again, read links in post #1. I do not have the knowledge to engage you on this topic.
moose4621:
I guess you need to read the links in post #1 for the answers to those questions and comments.
No, you need to answer those questions. What frequencies do you expect to be measuring with this equipment? Do you expect to see digital pulses with reasonably square edges? If so, you need to take a lot more care with the layout.
The thing is AC-coupled to begin with (see C1) so it won't show any DC component of any signal. It's not useful for measuring the majority of signals that I seem to use around Arduinos.
Again, read links in post #1. I do not have the knowledge to engage you on this topic.
Looking back at the original schematic, it does say "150V protection" on it. So that section should be isolated on the PCB and no other wires should cross that section. isolate the ground plane from that section. Plus both of the 150V sections should be isolated from each other. Personally, I would not put my computer on the line when I might forget this and plug it into something more than 150V.
Is there any chance that the output RCA plugs might be plugged into some other equipment? Or accidentally contact 12V or something? Like you unplug them and let them dangle into some active circuit? Then you need protection there to ensure your circuit isn't blown up. The pot is a good protection against most errors - always turn it down less than maximum after you disconnect and stop using the thing.
The comment on complexity mostly relates to 2-sided boards made professionally. They only charge by the square inch, not by number of holes or amount of copper, so everything you can do to make assembly easier (without making it bigger) will be free.
Speaking of holes, how are you going to mount this in a box? You don't want components with the possibility of 150V in a bare PCB strung across your desk. Mounting holes are very useful on all PCBs.
Have you heard of BitScope? I have one. I don't use it much but occasionally it's useful when I can't bring my big scope along. Their cheapest model has about the same limitations on voltage but it's much more capable.
MorganS:
No, you need to answer those questions. What frequencies do you expect to be measuring with this equipment? Do you expect to see digital pulses with reasonably square edges? If so, you need to take a lot more care with the layout.The thing is AC-coupled to begin with (see C1) so it won't show any DC component of any signal. It's not useful for measuring the majority of signals that I seem to use around Arduinos.
Looking back at the original schematic, it does say "150V protection" on it. So that section should be isolated on the PCB and no other wires should cross that section. isolate the ground plane from that section. Plus both of the 150V sections should be isolated from each other. Personally, I would not put my computer on the line when I might forget this and plug it into something more than 150V.Is there any chance that the output RCA plugs might be plugged into some other equipment? Or accidentally contact 12V or something? Like you unplug them and let them dangle into some active circuit? Then you need protection there to ensure your circuit isn't blown up. The pot is a good protection against most errors - always turn it down less than maximum after you disconnect and stop using the thing.
The comment on complexity mostly relates to 2-sided boards made professionally. They only charge by the square inch, not by number of holes or amount of copper, so everything you can do to make assembly easier (without making it bigger) will be free.
Speaking of holes, how are you going to mount this in a box? You don't want components with the possibility of 150V in a bare PCB strung across your desk. Mounting holes are very useful on all PCBs.
Have you heard of BitScope? I have one. I don't use it much but occasionally it's useful when I can't bring my big scope along. Their cheapest model has about the same limitations on voltage but it's much more capable.
Thanks again for your time, MorganS.
I'll try to communicate what I want to achieve.
I am at the very bottom of the arduino learning curve and continue to bite off more than I can chew.
I recently had a project where I was trying to drive a stepper motor at 0.1 rpm through to 100 rpm. I started with the stepper pot example in the ide, all good. Then went on to expand that to fit my project and I began to lose the max rpm and I wasn't sure why.
While pondering this, I thought it would be great to know whats coming out of the arduino and I happened across the xoscope site.
I quickly made up a lead with just 1m resistors on the end of the right and left channels of the mike input and instantly got usable pictures which when I rotated the pot, proved it was the serial out causing the bottleneck.
Ch1 = steps, ch2 = serial.
What a fantastically simple toy I had just come across. But I knew enough to realize that there was some inherent dangers in using the mike input the way I was and thats when I came across the buffer circuit which is the basis of this board.
Rather than build it using those preprinted development boards shown in the pictures on that page, with components boot strapped haphazardly all over the place, I thought why not extend my skills a little further and copy this circuit into fritzing and etch a custom board which surely cannot look worse than the original I was copying. (Is it)?
I also intend to 3dprint an enclosure for this with clasps to hold the board.
Then I could use xoscope with a little more confidence of not harming too much at least where xoscope was a usable option.
I also considered the plethora of cheap kit type oscilloscopes which may have been a better choice, I don't know.
One thing is for sure I, I could not justify the $150-$200 for Bitscope at this stage of my hobby.
I appreciate your words of wisdom, believe me, but I am willing to accept the apparently severe restrictions in usefulness that xoscope has at this stage at least. And no, I won't be scoping anything in the mains AC voltage range.
Oops, IMG
