I'm working on a little project. Actually, it turns out that it's a very big project overall, but the results are going to be well worth it. I'm designing an after school program for kids about or fast approaching the middle school age, and I'm planning to teach them about basic logic, through the construction of a 6502-based board, some basic programming, and then upgrading the board to do some simple video games..

Of course, I haven't played with the hardware side of this kind of thing since I was about the age of the kids I'll be working with, so it's been quite an experience already, and I've just started designing this project! As it happens, I need your help. ;)

The limitations

The kids I'm working with will not be allowed to use soldering irons. When I pitched the concept, I brought some solderless proto equipment (wire-wrap, breadboard, basic tools, etc) and you wouldn't believe the fast talking I had to do when they saw my DMM test leads! Oh man, I'm glad I didn't bring board saws and the like.

The second issue is going to be price. I'm playing with it at this point in a school where the kids' parents have got the cash to let their kids buy all of the kits, books, and trainers they want. I am developing it there because if it doesn't come across as a professional and educational program, I won't even be allowed to try out a pilot program.

I really want to take it to the schools across town where the opportunities for enrichment are sparse. Not only will it be fun to teach them, but it would really be good for the community as a whole and those neighborhoods in particular. Plus, I'm an undergrad and one of my two majors is K-8 education., so I can use this kind of experience.

I'm in contact with a couple of companies who might be willing to match what parents pay in parts. My time the kids will be getting for free.

The project

I've designed four stages into this thing:

1. Truth tables, basic logic. The kids build digital trainers using mostly TTL parts (CMOS has ESD issues we can avoid here) with an oscillator and dividers, switches, buttons, LEDs, counters, 7 segment displays, and solderless breadboard. Wire-wrapped, built in/on a pencil box. Cost around $30.
2. The kids prototype a simple 65C02 SBC on their trainer, then wire-wrap it, connect a very KIM-1 style interface, and learn some basic 6502 assembly/opcodes. The most expensive part is the 65C02 at $5.25 each, again close to $30 total.
3. We add proper keyboard and video and start playing with Forth, BASIC, or C (haven't decided yet). The microcontroller methods used by the Replica-1 for both could easily be done for under $30, but ASCII video isn't enough for later projects.
4. We get more serious with the programming. Hardware for this stage is limited to adding a noise maker chip and game hardware. First project for the new hardware: pong.

Other projects for stage four may include games that vaguely resemble other classics. ("Waka-waka-waka-waka", "The princess is in another mushroom!", etc), whatever I feel the kids can learn how to do from scratch.

I may try to write some stuff into the monitor for accessing a SPI memory device. MMC is a great candidate since I could interface it to a VIA pretty easily, although I probably will not be going for anything as complex as handling the FAT filesystem along with everything else in my 8k ROM.

The problem

Our RAM is all static, our ROM is EE, our *IA are the cheapest things I can use that'll get the job done. I really need a one-chip video solution like the microcontroller used by the Replica-1, but the only chip I know of meeting that definition are the MOS/CSG VIC chips. It doesn't seem you can actually buy these unless you pull them out of an old Commadore or something. That'd work to get me one to play with, but not for the kids.

Any suggestions what to use for video and where to get it? 320x200 and at least some color options are desired here, it'd be best if little interface hardware was needed, and anything I'd have to do SMD with is not going to work.

I'm stuck on this problem in a big way because I don't even know what video chips one can still get.

I wonder if you could add a stage before the first one (TTL parts) where you show the principles of logic using just switches. Or maybe using relays? You can certainly still get the parts for that! And I think it helps to make the logic more clearly visible, at least as far as the stage were you can write a truth table. Of course, you could use battery-powered lights for safety.

As for video timing generation, there's another post in this section that talks about using an Atmel AVR microcontroller to generate video. You'd have to treat it as a "black box" as far as the kids were concerned, otherwise they'd be confused by yet another programmable system. Same AVR solution could be applied to peripherals like joystick, mouse and keyboard.

In order to do what we want to do, I have to teach the kids a little about basic electronics. What's a resistor? A capacitor? Voltages, current ratings, rectifiers and regulators? If I had a low-end scope, I'd actually build a simple non-switching regulated supply and demonstrate with the scope.

I haven't got that, but I realized it is largely not necessary. The purpose of this is to get kids more interested in how computers work than in talking to weirdos on MSN, maybe teaching them a bit about programming and electronics and science in general in the process. Going back to DL and RTL, while certainly educational, don't fit with the program.

Unfortunately, I still haven't got a source for any PPU/VDP/GPU/etc designed for NTSC. Best ideas so far involve an AVR pretending to be a GPU, spitting out RGB, and attempting to use something else to get this into Y/C and composite NTSC outputs. The problem there is that the something else is usually packaged as a SOIC in modern times.

While its not color or graphic, I have created a simple NTSC B&W text display using an AVR. It may help get you started until the other comes along. http://users.softcom.net/darylr/io/vid3.html


As far as sources for the RGB to NTSC chip in a DIP package goes, I have found three part #'s in my searches. They are a Sony CXA1645 (24 pin DIP), NTE 879 (20 pin DIP), and the Motorola MC1377P (20 pin DIP).

Hope this helps.

Daryl

While its not color or graphic, I have created a simple NTSC B&W text display using an AVR. It may help get you started until the other comes along. http://users.softcom.net/darylr/io/vid3.html


As far as sources for the RGB to NTSC chip in a DIP package goes, I have found three part #'s in my searches. They are a Sony CXA1645 (24 pin DIP), NTE 879 (20 pin DIP), and the Motorola MC1377P (20 pin DIP).

Hope this helps.

Daryl

Make it with a Rockwell R6502. In the IC supply place in my area, they were cheaper. Plus, the 65C02 is CMOS, which I think you wanted to avoid, right?

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Sam

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"OK, let's see, A0 on the 6502 goes to the ROM. Now where was that reset vector?"