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Video Blog #018 - Building a Front Panel for an EDC-501J Voltage Standard

DISCLAIMER: This video is educational only, so if you decide to do the same yourself then you are on your own, I can't be held responsible for any problems/issues/damage/injury that may occur if you decide to follow this blog and try it yourself.


Whilst researching the idea behind designing and building a handheld Voltage Source I actually ended up buying an EDC 501-J Programable D.C Voltage Source. However, it was the remote programmable version without the front panel controls, so what better interim project to design & build my own front panel and retro fit it to the unit. Complete with LCD, pushbuttons & Arduino powered of course!

Since the video, I have found out how to enable 100mV mode on the unit, so the spec is now +/- 10uV (1ppm) for the 10V range, and +/- 0.1uV (1ppm) for the 100mV range. I've added another pushbutton to toggle between the two modes. I have also added a potentiometer to the front panel which gives the unit an alternative method to dial-up an output.

Also, thanks to some YouTube comments, it appears my unit came from the now decommissioned San Onofre Nuclear Generating Station.
SONGS = 'S'an 'O'nofre 'N'uclear 'G'enerating 'S'tation
SCE: 'S'outhern 'C'alifornia 'E'dison
NTD: 'N'uclear 'T'raining 'D'ivision.
More info here:-


Follow up video:




Whilst not a complete works of information, I have provided some detail and downloads below.

D0 - unused
D1 - 100mV/10V output to main board
D2 - D7 LCD
D3 - D6 LCD
D4 - D5 LCD
D5 - D4 LCD
D6 - Shift Out Clock (74HCT595)
D7 - Shift In Clock (4021)
D8 - Shift In Latch (4021)
D9 - Shift In Data (4021)
D10 - Shift Out Data (74HCT595)
D11 - E LCD
D12 - RS LCD
D13 - Shift Out Latch (74HCT595)
A0 - 0-5vdc from front panel potentiometer

The code requires two libraries, 'LiquidCrystal' which is part of the Arduino IDE already, the other 'TimedAction' which I have supplied in the ZIP. Works with Arduino IDE 1.0.5
Download here.

EDC501J schematics (selected ones annotated by me) - here.
Shift In (4021 IC) register schematic - here.
Shift Out (74HCT595 IC) register schematic - here.
AD550 IC datasheet - here.
Krohn-Hite Corporation - here
Operating Manual (includes schematics) for the EDC-501J (44 pages - Secions 1, 2, 3, 6 and additional schematics) - here
Operating Manual (includes schematics) for the EDC-501J (50 pages - Sections 1, 2, 3, 4 (Theory of operation), 5 (Calibration), 6, 7 (parts list), schematics) - here


PHOTOS (latest at top)

Some accuracy testing against my two Keithley 2015THD DMM's. I carried out this test at least 2 months after completing & calibrating the unit.....just to see how the accuracy was holding.
It looks like the worst I am seeing is 30uV/40uV out at the 5vdc output.
For sure the low TCR resistors I fitted in place of the original ones around the ref diode made all the difference in the world.




1 23456vdc


I added a pot to the panel thus giving an aditional way of setting the output voltage.
The mV/V switch now gives 4 states:
10V range
mV range
10v range from pot
mV range from pot
You can see the display in 'pot' mode in the pic below, and since the pot interfaces to the Arduino (2off dp's) the software still effectively controls the EDC DAC and thus what you see on the display is still as accurate. I.E. 5.00 actually gives 5.00000 vdc output.
I also replaced the banana sockets on the front with the original ones off the rear of the unit (better quality).









A few pics demonstrating accuracy. I have yet to verify my own DMM, and I have yet to tweak the EDC501J's pots to any real degree.








Since the video, I've found out how to enable 100mV mode, which gives 1ppm or 0.1uV resolution.



10V mode, which gives 1ppm or 10uV resolution.



The green switch is the 100mV / 10V mode toggle I added post video.



The build - Before:


The build - After: