I've juggled digital designs with different permutations of 5V and 3.3V devices on various occasions. I've also had to deal with the annoying SAA1043 which needed 5.7V minimum to meet spec. Also interfacing 4000 series CMOS at assorted voltages to TTL. There are always solutions, the art is finding something simple and workable.
For your design I was looking at ideas for running only the display at 5V while keeping everything else at 3.3V. Hence my ideas above. I don't think it can work with the display running between +3.3V and -1.7V as logic LO would be nowhere near adequate.
There is lots of stuff online about 5V<>3V3 interface problems and solutions. Just google "interfacing 5v to 3.3v logic".
There are LCD displays that will run on 3V3 such as :
https://www.sparkfun.com/products/9052 I'm not very familiar with different types of displays so have no idea about how they are driven etc. Also OLED displays:
https://uk.farnell.com/c/optoelectronics...ltage=3.3v
Excellent results Frank!
certainly looks good.
Jac
Hi Jeffrey
The more common type of 5V LCD can be converted to 3.3V operation see
here. I have done this conversion successfully to a 5V type while I was waiting for a 3.3V coming from china.
I tried the OLED types using both SPI and I2c interfaces. Compared to the parallel interface of the LCD they were slow to write to. I didn't get into it deeply but I suspect that the OLED types that I tried are wrote to pixel by pixel. Where the LCD HD44780 types are wrote to charter by charter.
Hi Jac
Thank you.
I didn't get much time to spend on it over the last few months but I am catching up a little now over the holidays.
Baring any surprises. I have the FPGA side of things finalised. I spent sometime aligning the video from the up converter and down converter with the syncs. This one of the things that I had left till last.
The FPGA is dependent on the microcontroller for the values that define the standard that is to be produced. Without the microcontroller working the FPGA cant work.
For construction or fault finding it would be helpful if the FPGA could work independently of the microcontroller. So I have stored a set of values in an array of std_logic_vector within the FPGA. This set of values can be loaded by pulling one of the FPGA pins that has been brought out to a header low. The FPGA will then produce 625 lines with a reduced amount of visible lines. I thought it best to use a reduce number of visible lines as it makes it clear that the converter is working. A poor picture below of the output.
Got some more done with the microcontroller as well, but there is still loads to be done.
Frank
And we are there!
I pretty much got it finished and it appears to be working OK. I have to get the webpage done up. I will post a link here when done.
Frank
(29-12-2020, 08:54 PM)`FRANK.C Wrote: [ -> ]For construction or fault finding it would be helpful if the FPGA could work independently of the microcontroller. So I have stored a set of values in an array of std_logic_vector within the FPGA. This set of values can be loaded by pulling one of the FPGA pins that has been brought out to a header low. The FPGA will then produce 625 lines with a reduced amount of visible lines. I thought it best to use a reduce number of visible lines as it makes it clear that the converter is working. A poor picture below of the output.
You can set signals to start at defined values after boot. Simple examples:
signal XYZ: std_logic := '1';
signal DC_OFFSET : std_logic_vector(9 downto 0) := "01010101010";
Otherwise registers are initialised at 0.
This can give similar behaviour to your method, but only at startup. It won't allow a preset to known values by pulling down a pin.
Your PCB looks really great. As always with software and FPGAs it's possible to make corrections and add new functionality simply by updating the code.
Excellent Frank, looking forward to seeing the design. I’ve built 4 Hedghog’s, 2 Vol’s, and just finished the picgen.
Mark.
Thanks Jeffrey.
Thanks Mark and welcome to the forums.
Wow that's a decent amount of equipment you have built. You have more Hedghog's than I.
Frank
Having more than one converter for a large collection does come in handy. I’ve got sets in different locations as well as on the work bench.
I built the Picgen in the same enclosure as the Hedghog and it works well through the Vol Modulator.
From you pictures it looks like you’ve used the same Hammond RM2015S enclosure which is nice.
This time the switches are not marked up so I wait to see how the user will interface all the functionality.
Mark
