We're back!

Sorry all, we've been on Holidays and now we're back.

I have a couple of projects going on but one is "secret" and the other is... trash... I'm trying to make art out of trash (or making less valuable trash out of more valuable trash).
The secret is something for my loved one (that's why it is secret), the trash one is a mini-wind generator, another of the projects involves LEDs, batteries, Solar cells and a jam jar and some other bits and pieces... Something like this.



I've noticed that postings are running low, at one per month.. I'll try to increase that this month to two... as any statistician would tell you, "it's a 100% increase"!! (and this one doesn't count, I promise!)

Some other projects in my head are around analog electronics, I've studying a lot of transistor circuits (band-gaps, differential pairs, current sources) and special op-amp circuits (integrators, analog computers). I'll try to post something on the matter later.

I've been unable to stick with the "cult of done" motto, 15 days is almost nothing in my development cycles. I have a lot of "diaper change" in between and it's hard to get some spare time during the week.

Meanwhile I also lost my beloved Rotring Quattro... two months after the blog post! Now I can't get used to the new one... it was my precious... I got a "cheap" (read not cheap) Parker Multi-pen Executive for replacement... The Lamy 4pen only comes with a 0.7mm pencil and I can't write with those, they're just too thick, kind of grocer's pencil...

Well back to work and I'll write soon..

SBC6120 with a teletype

Recently I bought a Teletype (a Texas Silent 700 model 703), it is special as it uses thermal paper and it is surprisingly silent :-).

I installed the light guides on the SBC6120 indicators, so now they are much more visible.

I had to replace an internal dip-switch and find a power supply for it, unfortunately I could not find a suitable power connector, for now it is connected with a pair of crocodile clips. The power input is AC-Earth-AC and a suitable voltage is from 20V to 26V, the current is about 1.5A.


The serial connection is at 300Baud surprisingly slow... 30 cps... This was how computers were operated before there were VDU (or CRTs as you prefer), it is very interesting. Next I'll try to install the Adventure game... The serial cable that came with the machine had to be tweaked in order to make it work with the SBC6120.


Here is a clip of theSBC6120 booting connected to the TI Silent.

SBC6120 - Project Done!

It is done! My SBC6120 finally has a case that I am proud of. It still needs some finishing touches (namely some light pipes for the LEDS on the board to the front panel), but that's about it.


Since I haven't used it for quite some time I forgot some of the "intricate" details of working with it:
- I lost an incredible amount of time in a hardware bug that did not exist, simply because I forgot that the communication interface is 9600-7E1 and NO handshakes (hardware or XON-XOFF)... Minicom in linux installs default with hardware handshake, you see the boot message but you cannot write anything...
- and OS/8 only works with CAPITALS... (This is not a MAC OS8!, Mac friends look elsewhere).
To fit everything inside the Hammond box, I built a base in 1.5mm plastic and glued nylon screws upside down, these would fix the SBC on the lower part of the case, I've built a power supply board to convert 12V in the 5V needed for the SBC, finally I designed custom front and back panels.
I've built four prototypes of the front panel (in paper) and glued them to 2mm thick foam to get a look and feel of the panels before committing to fabrication. I used the services of Schaeffer AG for milling the front and rear panel, their (freely distributed) CAD program is actually very nice and it is available for linux! (I had some problems with sending the design but the drawing was actually all done in linux). It isn't cheap, but sure is top-quality.


The reset button does not protrude to the external of the box as intended, but having a "insert pencil here to reset" hole is not so bad (might even be a feature :-). Here you can also see why there's a need for a light pipe.



The slots in the back are enough for cooling the SBC6120 and the 3.5'' IDE drive, it takes about six hours to serially download two disk images, the boards and case never exceeded ambient temp by more than 20C.


The whole case is quite small (for a PDP-8), here's a top view, a fair view of what's inside is in an older post and here. The paper sheet below is A4 size.


The final photo just like in Sparetimegizmos is my the SBC6120 with an HP-16C side-by-side, just like the "inspirational photo" from their site. Yes, the calculator is more expensive than the computer :-).


Next... Install some adventure games... like this one... :-)
what's the use of a computer other than entertainment....

The Calculator is dead, long live the Calculator...

My eyesight problem triggered a new blog motto... I must stay away from the computer when I'm "dedicated" to my home projects (or at least reduce the time to a minimum).
Here it comes "Never again use a Spreadsheet for designing power electronics"! I must admit that for work it is the best thing available,test scenarios, test components, circuit configurations everything numerical at a touch of a "button". But I don't need that, this is supposed to be for fun. I don't need speed of calculus, I want to keep learning the "Art". From now on calculations will be displayed scanned from the squared paper (I still have to find a scanner though)... And these two will have a bit more work...

Thinking back, how many times did I use a graphics calculator for a graphics problem? I don't remember, but not many...
I did love my HP48 in the last two years of university (before that I had a TI 57 II), I had to work for a while to pay for it and my father helped out with 50%.
Once at an exam, the teacher that saw my Texas classified it as "a Grocer's calculator", that was really embarrassing and this was in 1997!(most of my colleagues had either an 48S, the 48SX or the Casio Computer 850??)...
The HP32S was bought recently in Epay, to get something a bit more "portable" and keep "playing" outside...