Altair-Duino 680 Assembly

[Charles Wall]

I assembled my Altair-Duino 680 a couple of weeks ago thinking I had done a good job, even checked it twice.

Upon power-up, I ran into a problem.  The lower 8 address lights stayed on regardless of the switch settings.  I assumed those LEDs were controlled by one of the 3 ULN2803As.   

I loaded BASIC and it seemed to work except when I typed text in BASIC, I saw duplicate characters on the screen.  I was using Putty.  I seem to remember some discussion a few months back on the forum about duplicate characters but don’t remember what the solution was.

I contacted Chris who added the schematic to the web site and sent me some suggestions of things to check regarding the A0-A7 address lights being on all the time.  I am embarrassed to say it tuned out that I had installed U3 backwards even though I had checked it twice!  

While correcting the U3 orientation, I also corrected the pinout for the serial port as shown in the ADDENDUM on the web site.  These changes cured the A0-A7 address lights being on and for some reason cured the duplicate display of characters being typed into BASIC, although I don’t know why character input in BASIC was affected.

Now I am seeing another problem.  When I attempt to CLOAD a program from the SD card I get an error message that the SD card is not ready and the 680 goes to LaLa land.  Reset does not function, and I have to power-down and power-back-up to get the 680 to respond.  I checked the seating of the SD card and pulled the SD card to check and be sure the files were present which they were.  I also checked the orientation of the SD card module and resoldered the 12 connections on the right-angle male header.

Chris told me after I load and start BASIC make sure all address toggles are down (off) and then toggle DEPOSIT DOWN.  I should get a listing of ,BAS files on the SD card.  I did not get the listing.  In fact, nothing displayed.

Chris suggested I move this discussion to the forum rather than private email.  He also asked me to send a picture of the SD card module to him which I did.

Any suggestions would be appreciated.

 

[George W4AVO]

In ref to the CLOAD problem- Check the installation and solder of the 6 pin female socket on the circuit board in the center of the Due footprint. It's easy to miss. Ask me how I know!

George

[Charles Wall]

I checked; the 6-pin socket is there.  I pulled the Arduino and resoldered the socket.  Still no go with reading the SD card.

Thanks, all input is appreciated!

[Chris Davis]

I'll send another SD Module (they're cheap).  I guess at least we can eliminate that as a problem.

[Chris Davis]

Why don't you install the latest software just to make sure that's not the issue: https://adwaterandstir.com/install-680/

On Friday, December 5, 2025 at 1:39:13 PM UTC-6 wall...@gmail.com wrote:

[Charles Wall]

Would you send a right-angle header also?  I don't want to damage the board taking the old one out, I will cut the pins and take them out one by one.

I will reload the software later this afternoon and see what happens.

Thank you.

[Chris Davis]

Yes, I sent the header as well.

[Charles Wall]

I reloaded the software, and it behaves differently but still doesn't work.

When I toggle DEPOSIT DOWN with all address switches down, I get "Attempting to load /BAS/FILE1.TXT..." followed by "No SD Card Present". When I try the CLOAD "23MATCH" command I get "(CAS) LOAD aborted: SD not ready".

[Chris Davis]

If it's attempting to load FILE1.TXT then it's detecting that SW0 is up.  Switch to HLT mode and see if the address LEDs illuminate based on the switch position.  This issue would be separate from the SD card problem.

[Charles Wall]

My error.  Yesterday, I apparently forgot to turn A0 switch off after loading BASIC.  I retried today and it gives the load FILE1.TXT error with A0 on.  If I try with A0 off as I should have done, I get no response.  Sorry for the confusion.

[Charles Wall]

I received a new SD Card Module today and installed it.  I can now access the SD card!  Apparently, I had a bad SD Card Module.  Thanks, everyone for your help!

[Chris Davis]

That's awesome news!