forward voltage testing of diodes using arduino

[DavidFet]

Apologies if this is in the wrong forum sub, my first post at DITStompboxes 

I made an arduino shield that allows you to test the forward voltage of diodes, looking to test some dodgy GEs I got off aliexpress.
https://github.com/david-sg/arduino-diode-forward-voltage

GE 1N341 (#1)
Wait
Start
VCap:4.55 Diode FV:2.41 Current:10.69
VCap:4.46 Diode FV:2.37 Current:10.47
VCap:4.13 Diode FV:2.23 Current:9.50
VCap:3.48 Diode FV:1.94 Current:7.69
VCap:2.95 Diode FV:1.69 Current:6.27
VCap:2.52 Diode FV:1.49 Current:5.15
VCap:2.17 Diode FV:1.31 Current:4.27
VCap:1.88 Diode FV:1.17 Current:3.54
VCap:1.64 Diode FV:1.04 Current:2.98
VCap:1.43 Diode FV:0.93 Current:2.49
VCap:1.26 Diode FV:0.84 Current:2.10
VCap:1.12 Diode FV:0.76 Current:1.78
VCap:1.00 Diode FV:0.69 Current:1.51
VCap:0.89 Diode FV:0.63 Current:1.29
VCap:0.80 Diode FV:0.58 Current:1.12
VCap:0.72 Diode FV:0.53 Current:0.95
2ma Diode FV: 1.04

GE 1N341 (#2)
Wait
Start
VCap:4.52 Diode FV:1.52 Current:15.01
VCap:4.41 Diode FV:1.50 Current:14.55
VCap:3.96 Diode FV:1.44 Current:12.62
VCap:3.12 Diode FV:1.30 Current:9.06
VCap:2.52 Diode FV:1.19 Current:6.69
VCap:2.09 Diode FV:1.08 Current:5.03
VCap:1.77 Diode FV:1.00 Current:3.83
VCap:1.52 Diode FV:0.93 Current:2.95
VCap:1.32 Diode FV:0.85 Current:2.34
VCap:1.17 Diode FV:0.80 Current:1.86
VCap:1.04 Diode FV:0.74 Current:1.51
VCap:0.95 Diode FV:0.70 Current:1.25
VCap:0.86 Diode FV:0.66 Current:1.03
VCap:0.79 Diode FV:0.62 Current:0.85
2ma Diode FV: 0.93


Its a fork of this page for some background:
https://www.lightofdawn.org/blog/?viewDetailed=00187#prettyPhoto

It seems to be working, but I wanted to see if others got similar results, and if what I was getting was accurate (for these GEs anyway, VF seems high, so probably not the type ordered?)
Also, any and all comments on the perfboard, or code is most welcome! Anything I can improve?

Thanks!

[DavidFet]

Results from an 1N4004
Wait
Start
VCap:4.50 Diode FV:0.71 Current:18.92
VCap:4.36 Diode FV:0.71 Current:18.24
VCap:3.80 Diode FV:0.71 Current:15.45
VCap:2.80 Diode FV:0.70 Current:10.50
VCap:2.12 Diode FV:0.67 Current:7.23
VCap:1.67 Diode FV:0.66 Current:5.05
VCap:1.36 Diode FV:0.64 Current:3.56
VCap:1.14 Diode FV:0.63 Current:2.54
VCap:0.98 Diode FV:0.61 Current:1.86
VCap:0.86 Diode FV:0.60 Current:1.34
VCap:0.78 Diode FV:0.58 Current:1.00
VCap:0.72 Diode FV:0.57 Current:0.76
2ma Diode FV: 0.63

[mozz]

 I don't really know if any germanium's diodes are made today, most likely they are shottkies?

[iainpunk]

I don't really know if any germanium's diodes are made today, most likely they are shottkies?

in contrast with Ge transistors, the diodes are still produced, mainly for radio purposes.
Ge diodes can seem to have such a high forward voltage, when the current is so high as OP uses, especially since the internal resistance is quite high.
in radio use, the currents are in the single digit uA- range, not the mA range OP measured it with.
schottkey diodes have way lower resistance and wouldn't get up to 2.5V at 10mA

cheers, Iain

[mozz]

I can only find 1 current manufacturer of these, 5 different ones is all. Mouser/Digikey in the US carries none.

1 large seller even states this for 1N34A.
"Note: These are PN junction silicon types and NOT point contact germanium."

AMERICAN MICROSEMICONDUCTOR INC is one of the few suppliers of germanium diodes in the world; we have been supplying these parts to the largest manufactures in the world over the last 30 years and we continue to be one of the largest suppliers worldwide. We support this diode and plan to continue to do so into the distant future.

[DavidFet]

Heres output from a shottky 1n5819
VCap:4.49 Diode FV:0.26 Current:21.14
VCap:4.34 Diode FV:0.26 Current:20.39
VCap:3.72 Diode FV:0.26 Current:17.29
VCap:2.59 Diode FV:0.25 Current:11.72
VCap:1.85 Diode FV:0.24 Current:8.01
VCap:1.35 Diode FV:0.23 Current:5.57
VCap:1.00 Diode FV:0.22 Current:3.91
VCap:0.77 Diode FV:0.21 Current:2.76
VCap:0.60 Diode FV:0.21 Current:1.95
VCap:0.48 Diode FV:0.20 Current:1.39
VCap:0.39 Diode FV:0.19 Current:1.00
VCap:0.33 Diode FV:0.19 Current:0.73
2ma Diode FV: 0.21

photo of the supposed 1n34a







I also found this LED to give interesting VF. its a flickering LED, so its got something onboard to create a random flickering affect. Clipping seems warmer to me than a red led.
https://www.aliexpress.com/item/32782781815.html
VCap:4.51 Diode FV:0.87 Current:18.19
VCap:4.38 Diode FV:0.86 Current:17.55
VCap:3.84 Diode FV:0.84 Current:14.97
VCap:2.86 Diode FV:0.80 Current:10.30
VCap:2.19 Diode FV:0.76 Current:7.15
VCap:1.74 Diode FV:0.73 Current:5.08
VCap:1.43 Diode FV:0.70 Current:3.61
VCap:1.20 Diode FV:0.68 Current:2.61
VCap:1.04 Diode FV:0.66 Current:1.88
VCap:0.92 Diode FV:0.65 Current:1.37
VCap:0.84 Diode FV:0.63 Current:1.03
VCap:0.78 Diode FV:0.63 Current:0.76
2ma Diode FV: 0.68

[Rob Strand]

in radio use, the currents are in the single digit uA- range, not the mA range OP measured it with.
schottkey diodes have way lower resistance and wouldn't get up to 2.5V at 10mA

+1.  The 10mA test is by far the most reliable way to separate the Ge's from Schottky's.   It's an easy test to do.

Reply #6 on this thread shows some 10mA test results; my Ge's were around the 1V mark @ 10mA,
https://www.diystompboxes.com/smfforum/index.php?topic=117550.0

Reply #11 has original curves for a number of Ge diodes, including some very early (maybe Nov 1947) Sylvania 1N34 curves (which have about 1.1V @ 10mA).