VDI-RODERICO

[roderico]

you are all welcome, I only wrote the code for the microchip compilers, the original schematics was borrowed from the idx thread.
Currently there are drivers for the following display controllers:

- HD44780 for 16x2 LCDs and similar displays
- KS0108, RA8808, ... 128x64 GLCD displays
- S6B0108 same as KS0108 but with CS1, CS2 logic inverted
- ST7567, ST7565 with the intel 8080 MCU parallel interface

you might also add the SSD1305 to the list and show the universal display board. Below it is the source code for v2.1+ST7567 driver (never released because it was for v2.2) but when I implemented I had to reorganize the code to make it easier to add new display drivers, this could help for the SSD1305 since you only have to re-implement the functions of st7567.c or ks0108.c e.g. in a new file ssd1305.c, probably these are the functions you have already implemented. IMO, the only concern with the OLED display is the visibility with direct sun light but we would not know until the field testing.

The current vdi does not perform well with weak signals, I think this could be improved by increasing the dynamical range of the ADC, e.g. with some kind of variable gain amplifier or with an external switch to increase/decrease the gain of the MCP602. IMO, for the LOBO/TGSL you would need at least to tune the gain for X/Y channels as they might be different from the IDX, e.g. kroman01's A-B points for LOBO should give different values to the ADC. You could use the scope view with auto scale off (1x or 2x) or an oscilloscope to tune the gain.

[waltr]

Here are the .h & .c files for the SSD1305 display I used. This is available from Adafruit in NY, USA:
https://www.adafruit.com/product/2719

Also a pdf of the UniverDisplay board schematic and PCB Gerbers.
This has many options so I install parts as needed.

The op-amps for the VDI I put on a separate board and is not included.

The reason is that I need from time to time a display for some project. Now I have a PCB that is adaptable to various projects. Also the newest PIC 28pin from microchip is the 18F2xQ10 which has PPS (allows pin swapping or assignment) plus other features.
Another I have a few of is the 18F2xK42- this has PPS an NCO (handy to generate audio), and a 12bit ADC.
Both these newer PICs cost less than the ones used for the VDI.

[roderico]

ok thank you, this driver could be added to v2.2 with small modifications if there is no problem from your side. Porting the code to newer pics is not a problem, I think pic18f25k22 was not very expensive not long ago. 12-bit ADC would be better but might not solve the problem with faint or deep objects and you might need to change integer maths to accommodate more bits, I was proposing a more simple test without the need of changing the firmware, i.e. just to increase the gain of the MCP602, the side effect is that it will saturate sooner, so a variable gain would be perfect for this and might fix the problem

[roderico]

on a second thought, increasing the gain would also amplify the noise, so it needs testing to find optimal values...

[waltr]

ok thank you, this driver could be added to v2.2 with small modifications if there is no problem from your side. Porting the code to newer pics is not a problem, I think pic18f25k22 was not very expensive not long ago. 12-bit ADC would be better but might not solve the problem with faint or deep objects and you might need to change integer maths to accommodate more bits, I was proposing a more simple test without the need of changing the firmware, i.e. just to increase the gain of the MCP602, the side effect is that it will saturate sooner, so a variable gain would be perfect for this and might fix the problem

I posted the code here for you or anyone to use. So please do add the ssd1305 code.

Correct, simply more gain in the op-amp (602's) would not be the cure all.

Adding a diodes or a bipolar in the op-amp feed back (log amp) may be better.

[dbanner]

I posted the code here for you or anyone to use. So please do add the ssd1305 code.

Correct, simply more gain in the op-amp (602's) would not be the cure all.

Adding a diodes or a bipolar in the op-amp feed back (log amp) may be better.

I wondered about those log amps in the whites5900/6000DI as a possible front end, combined with those x and y preamps from the same detector. More circuitry, yes, but perhaps more stable and improved performance.

[roderico]

are the schematics of that part of whites5900/6000DI available somewhere?

[roderico]

SSD1305 code would not be compatible with v2.x without the universal display adapter this is more for a major version e.g. v3.x with newer pics and/or displays as it needs a new pcb, but still can be used as extension for v2.x as explained in waltr's post which is very well done and explained and no need for modification

[dbanner]

are the schematics of that part of whites5900/6000DI available somewhere?

You'll find the log amps circuits in here along with the entire VDI circuitry, from the X/Y straight through to the meter drive.
I note there are diodes but what stands out is the use of dual transistors (matched) in a single package (probably for accuracy and stability) on both sides of the log amps. Now that's good engineering.

[roderico]

ok thank you, the goal here is to filter out the noise or subtract the background of weak signals to increase the signal to noise ratio and move it to the ADC range, maybe just adding the diodes and adjusting the band filter would improve it, it would need more testing...

[roderico]

I haven't done any test but the log amp probably won't work because the output voltage would be proportional to the log of the input and then pic would compute the ratio of X/Y to extract the phase and with the log ratio we cannot have the angle, in this case we need a linear amplifier unless a log-1 is done before

[dbanner]

You are correct. The output of the x and y log amps outputs (Vout1 and Vout2) are fed to a difference amplifier with a gain of 10. I am not expert here. But I assume one can replicate the mathematical functions in the software.
There is something referred to as logarithmic-ratiometric ("log-ratio"). Compressing the signals seems to offer some benefit in terms of precision. The DC log amp transfer function seems to be very good for this task(VDI measurements). There are even chips (max4206) which are dedicated to this purpose.

[dbanner]

Here is the exact same circuit topology I found in an article. Perhaps all the software needs is a good ratiometric table for referencing the signals. I know little on this topic, so please forgive the shallow explanations.

[roderico]

all this can be done by software if we know the exact algorithm, the differential amplifier would compute the difference of the log amps, i.e. except from constants, log x - log y = log (x/y), do they use just log(x/y) as a vdi?

[dbanner]

Well there is what appears to be an antilog amplifier?? after the differencing amp.(whites log amp and meter VDI circuit). So there is some math going on here all the way through. A series resistor at the inputs to the log amps (voltage input device) converts to a proportional current. These are current sinking (NPN) log amps.