VDI-RODERICO

[roderico]

I updated the schematics to include the 2.5V voltage reference, however, this does not scale with Vdd, i.e. for 3.3V you need a 1.65V reference, I also increased the capacitor values and added an optional input for 78L05 (or better regulator) and changed back the values for the MCP602 that are more tested, this latter could be improved with something similar to SWL's mod.

[waltr]

Looks good.
Thinking for a 3.3V Vdd one could use an adjustable Voltage reference for the MCP602s.
The LM431 type reference comes to mind. There are others with a 1.24V minimum, just don't remember the part number.

[roderico]

I think the minimum for LM431 is 2.5V, 1.24V might be fine, but there is always the resistor divider at the last resort. I just had a look at TGSL schematic (v3) and assuming you connected the vdi to the output of U103a and U103b a possibility could be to calibrate it with J3 in "All metal" in that way you would have a reference when you are using the disc mode (by switching to all metal).

[Altra]

Been following the thread with interest, many of the newer pic's have built in references

I bought some pic16f1788's and never did anything with them. They have op-amps, 12bit adc with built in references including a 1.024v, 8bit dac etc. It would be interesting to see if you could make a complete vdi meter with the internal op-amps, reference, a few external capacitors and resistors.


http://ww1.microchip.com/downloads/e.../40001675C.pdf

[roderico]

That would be very good for a v3.x because you would save the MCP602 and the external voltage reference reducing the number of components and costs, however there were also some other suggestions for replacing PIC18F25K22 and IMO a compromise between improvements, required work and cost is needed before selecting a new pic. PIC16F1788 only have 16KB of program memory we need at least 32KB.

[Altra]

That would be very good for a v3.x because you would save the MCP602 and the external voltage reference reducing the number of components and costs, however there were also some other suggestions for replacing PIC18F25K22 and IMO a compromise between improvements, required work and cost is needed before selecting a new pic

The PIC18F25K22 has the same adc voltage references as the 16f1788, so a good choice it can also run at 64mhz. I saw your photo of the zoren glcd above, nice graphics! I have mine working now also. No problem operating from 3.2V - 5V also added a pnp to switch the backlight on and off. The emitter connected to +5, I used a 100 ohm resistor between the collector and the led anode. I ordered 3 more displays about the time the coronavirus breakout, probably won't receive then until March or April?

[waltr]

I think the minimum for LM431 is 2.5V, 1.24V might be fine, but there is always the resistor divider at the last resort. I just had a look at TGSL schematic (v3) and assuming you connected the vdi to the output of U103a and U103b a possibility could be to calibrate it with J3 in "All metal" in that way you would have a reference when you are using the disc mode (by switching to all metal).

Just checked my inventory and it is a ZR431L that it the 1.24V version and adjustable from 1.24 to 10V.

That is an idea to calibrate. However, I found that the X-Y plot was much more useful than the VDI Number when in the field and deciding to dig or not.

Bad news is that the second OLED display simply Stopped working the other night. Same happened to the first display but a 'one off' and having a spare didn't seem a big deal. Having a second display just stop working is killing me.
No idea why since no connection or code changed. Just, its working, turn off, turn on -nothing!
Scope says all signals from PIC to display look ok.

[roderico]

The PIC18F25K22 has the same adc voltage references as the 16f1788, so a good choice it can also run at 64mhz. I saw your photo of the zoren glcd above, nice graphics! I have mine working now also. No problem operating from 3.2V - 5V also added a pnp to switch the backlight on and off. The emitter connected to +5, I used a 100 ohm resistor between the collector and the led anode. I ordered 3 more displays about the time the coronavirus breakout, probably won't receive then until March or April?

the zolen display should work well with the latest schematics, I think PIC16F17xx are the only 8-bit mcu with internal op-amps, but the firmware will not fit in PIC16F1788 (only 16KB) and PIC16F1778 (28KB) has no internal voltage references, the other option is to move to 3.3V (as waltr) and 16-bit but it would break compatibility with KS0108 displays...

[roderico]

Just checked my inventory and it is a ZR431L that it the 1.24V version and adjustable from 1.24 to 10V.

That is an idea to calibrate. However, I found that the X-Y plot was much more useful than the VDI Number when in the field and deciding to dig or not.

Bad news is that the second OLED display simply Stopped working the other night. Same happened to the first display but a 'one off' and having a spare didn't seem a big deal. Having a second display just stop working is killing me.
No idea why since no connection or code changed. Just, its working, turn off, turn on -nothing!
Scope says all signals from PIC to display look ok.

then maybe there is some pin in the display to control the contrast that you need to configure similary to the ST7567...

[waltr]

then maybe there is some pin in the display to control the contrast that you need to configure similary to the ST7567...

Nope, there is not contrast control on OLED.
My current theory is the Boost convert chip died. There should be 13V to drive the OLEDs.
It seems to be a fairly standard 5 pin SOT so maybe another will work.

[waltr]

Yes, the Boost convert chip on the OLED display died. Temporary fix is very easy. Simply solder wire on the boost output, at cathode of diode and fee with 12V. Display now works.
Actually, Newhaven Display has this as an option on their OLED display that allows disabling the on-board boost converted and supplying 14V from external source.

[roderico]

good to know the problem and the fix, do you know if this is a common issue of all OLED displays or just a specific problem of some models?

[waltr]

good to know the problem and the fix, do you know if this is a common issue of all OLED displays or just a specific problem of some models?

Seems to be a problem with only Some batches of the same OLED. I did post on the Adafruit forum, bought from Adafruit, and Customer support stated many 100's have been sold and only a few have died. A forum search only came up with four having similar issue.
They also offered a refund for the two displays and suggested I Not buy that one again.
Here is a thread I posted on Adafruit with details of the fix:
https://forums.adafruit.com/viewtopic.php?f=47&t=161883

So it seems that this is not a common issue but simply the luck of the draw, or many chip batch, of the Chinese made units..

I did get out detecting for about fours hours today. Display worked without issues.
Today was a local park so more trash than rusty stuff. I am starting to get a better 'feel' on target ID and got to Call the target correctly. Still lots of junk targets, like can slaw, in the low-mod VDI numbers that could be a good target. I do like Nickles and rings so must dig the junk.

[roderico]

maybe it is just bad luck as you say but these displays are very expensive to fail like this (bad quality components?) a refund makes sense, anyway, very good work of debugging the problem, finding a fix and very well documented in the above link.

[waltr]

maybe it is just bad luck as you say but these displays are very expensive to fail like this (bad quality components?) a refund makes sense, anyway, very good work of debugging the problem, finding a fix and very well documented in the above link.

Thanks. Just got a notice that they refunded the purchase.

The weather got much better yesterday so got out to the old Farm site. I have hit this place hard for three year but know there is more hidden in the iron junk. So went slow an seep from multiple angles look for and indication of a non-ferrious target.
The X-Y display is excellent for this. With bit ferrous and non-ferrous close the X-Y graph does not show a straight line but the line will curve or bend. Digging these signals did find non-ferrous items along with ferrous. Many were .22 shells (brass) but did get a few great items.
One was an 1865-1889 3 cent nickle (70% cu, 25% ni the diameter of a US dime but thinner).
Best find was an 1813 1st Regiment of Artillerist button. For this button I dug 6" (15cm) down and found an Ox shoe. Re-sweep and now a clean signal. another 3" (7.5cm) down was the button (20mm diameter).
The VDI numbers were uncertain and changed at different sweep angles.Other good find were Early 1800 buttons and the chape from a shoe buckle. In all 5 great finds.