DIY 8bit computer

I’ve had a couple of 680x PIA chips laying around. Every now and then I come across a DIY retro 8bit computer project and makes me want to build one. So I went ahead and bought a 6800 CPU and a couple of 74s189 SRAM chips.

A while back I had sent off for some TerminalScope PCBs and they have been sitting collecting dust in a box somewhere. I guess I can toss one together for the 8bit computer.

While I was shopping for the SRAM chips I came across some z80 compatible PIA chips. It was 15 bucks but it comes with ten ICs. So maybe down the road I can build a Z80 based system with CP/M

In all I got a lot of info from Grant Searle’s website. He has a few small chip count mini 8bit computers that can be built on bread boards.

Right now im awaiting parts so I can start. In the meantime I am researching and thinking of a few things such as power supply and storage. I am thinking of a simple linear supply and making sure I have filter caps at every chip’s V+ and ground pins. Also im leaning towards Compact Flash for storage since it is a Parallel device. Doubt I could get Ethernet with a TCP/IP stack on it so simple direct connection via Serial should be plenty. I think I have a MAX232 chip in my junk box. If not I could use a 7404 Hex Inverter for it or for fun use some switching transistors and resistors. It would be fun to have an array of switches to control functions kinda like the Altair 8080. I’ll just add some LEDs to the inputs and outputs for some blinken lights.

If anything on the final build I can add the TerminalScope circuit to the mainboard. It’s a dirty way but the easiest without using too much system resources.

Keithley 179

I acquired a Keithley 179 Ture-RMS bench top multimeter. The case is a smokers beige and has a few scratches here and there. The date code on the IC chips are dated from 1978 so it’s an early revision.

When I received it I took the top off to take a look around and sure enough the filter capacitors were leaking electrolyte everywhere. I went ahead and powered it on and it some what worked. I don’t have any voltage references or resistance references to see how far out it is but comparing it with a cheap none True-RMS meter it keeps up.

Today I recapped the whole unit. Since RadioShack was having another store sale off they had the electrolytic caps I needed, not to mention the axial type as well. They didn’t have any tantalum caps so I had to use electrolytic caps instead but the two caps I changed are only for filtering so it works just fine. The other two tantalum caps still had fine ESR and checked out fine so those were the only two polarized caps I left in. While I was at it I replaced the two probe banana jacks since the old ones were corroded.

Some time I might sand down the case and paint it. Maybe even make a custom front bezel instead of the translucent red panel.

Arduino project

I got a nifty idea of a universal device controller to use with the Arduino. It is gear towards test equipment but it could be used for other things. When I say test equipment I’m talking about power supplies, function gen, and maybe even multimeters.
It doesn’t have to be fancy of a setup like a touch screen and I2C hardware but simple a simple LCD and push button switches.

My take on this will use the TVout Library so I can use one of my many 7inch LCDs I keep finding at thrift stores. A simple 4×4 keypad array will work fine and maybe even use a smaller or bigger keypad if needed. There are also a few libraries that use the analog pins of a Arduino to control a keypad via voltage dividers. The fun part is keeping the pin count down to leave for expansion or maybe use some 74HC595 8bit shift registers.

This will be used for my bench power supply and also I plan to build a Function Generator kit to modify as well. In an older post I modified a Voltmeter sketch that uses the TVout library and maybe with some code changes I could add other options and make something of a multimeter. Maybe I could modify a cheap handheld multimeter to use the controller.

So here is the specifications for this project.
TVout support for the video.
PWM to DAC converter to control analog signals.
Keypad controlled with analog pins to keep the digital freed up for more control options.
Relay control for controlling power sources such as AC or output supply from a DC supply.

I’m thinking if I should use a TIP122 Darlington transistor or a ULN2003 transistor array for the PWM to DAC control. I could use the 4n35 opto but I don’t have any in stock.


Building an case for my cheaper transistor tester

I have one of those cheap Chinese transistor tester kits. Today I decided it needs a case. I have a case from a CB radio that will work very well to house the tester. At the moment I have to use cardboard for the front bezel until I can get some plastic or a decent blade for the jigsaw to cut some sheet metal. I plan when finished to paint it to match the rest of my gear or I could keep it with the fake wood panel look.

To make this work I had to modify the circuit board a bit such as replacing the female header for the LCD to make pins so I can use a ribbon cable to extend the LCD. The tactile switch was also removed with some wire to extend the button to the front bezel. While I was at it I removed the brightness pot and put on a typical 1/2 watt 15k pot so I can mount it to the front bezel as well. I just hope after recalibration it will work properly. Right now it sees thins with a 2 ohm resistance.

As you can see I finished it. Some acrylic paint helped a lot on the cardboard bezel. Also recalibrating it worked well. It now rests under my scope.

News 1/31/17

It has been a month with the new job and it is still awesome compared to the old one. Stress free, I’m basically my own boss and I pretty much control my paycheck.

The other day I spent time with the youngest son and both played around with some R/C cars. We got a couple of cheap ones from Walmart. Afterwards I rebuilt my car and made it a hell of a lot faster. Tossed in a old control board I had in my junk box and changed out the odd 4.5 voltage rated caps to higher voltage caps that matched the Micro Farad rating and tossed on a 8 volt battery.

The Desktop CNC project is slow going still. I am taking my sweet time with it so everything will work correctly.

In the mean time I came across a old JCPenny CB radio and stripped it down for parts. The case will be reused for my Component tester. The fake wood and flat head screws have a neat old school look.

Other then that I have been spending more time with the family since I am home in the evenings now.

Table top CNC update.

When building a CNC from wood it can be very challenging. Unless you have a full fledged wood shop. With basic tools that most people like me have it involves tons of sanding to get a level surface. Not to mention a bunch of measuring and remeasuring to make sure you get a proper straight cut. The router table setup I have works well to straighten up most of the cuts but everything else requires tons of hand sanding. I’m tempted to buy a electric sander before doing anything else. Now this isn’t because I went with OSB for the material, this is the challenge for any kind of wood.

I came across an awesome circuit for the Spindle. The circuit ramps up the speed of the motor when the RPMs hit a certain speed. Or should I say when the motor bogs down it adds more juice. I got this from a YouTuber called MrJohhhnnnyyy.

drill  One thing that isn’t shown on the schematic here is you need a Diode to go across the motor terminals for added protection. I doubt 40V is needed to drive the circuit, I am planning to use a old laptop charger to power it. I could always use a small transformer that is rated for 40 volts, an bridge rectifier and boost up C1 to a higher capacity or add in a second filter cap.

I worked on the Y-Axis a bit. The railing I have is too flimsy to use so I found some old drawer handles. I sanded the paint off and polished it with 2000 grit sandpaper. It came out real nice and now I need to mount the railing. Before mounting them I need to find something to use a bushings. I could use some bearings I pulled from old hard drives but it would cause more time to setup for them to run perfectly parallel.

Table top CNC prototype

Today was a good day. I worked on the CNC for a bit while ever so taking my time. When you create a one off prototype you have to really plan things. I don’t like to sit at the computer fighting SketchUp for designs. I prefer to take the material I have and physically draw the layout and put it all together as I go. This way if I run across a problem I can quickly resolve it.

I worked on the Z axis a bit today. When I was thinking of game plan I decided to use a hard wood for the base that will hold the spindle. The vibrations with OSB might loosen things up over time.


Since the back piece of the Z-Axis is OSB I made sure to use the ruff side the glue side so the glue can adhere better. The piece of Oak is pallet wood. I let the glue setup enough that it was squared and remove it from the workbench. I re-clamped to itself and letting it cure overnight so I can pre-drill and secure it with screws. I wish I had enough Oak to do the whole Z-Axis but as long as the spindle mount is solid it should hold up. I’m not planning to use a Dremel or anything like that for milling/routing.

These rail pieces I found last week. I think they were from some can light fixtures. They were sticking in the dirt at a job site. I cleaned them up and filed down the high ruff spots until they slid true. These will be the glide rails for the Z-Axis.

I did a test fit for the X-Axis glide rails. I was a bit off but a simple fix with the router table fixed it. I plan to do a friction fit for the glide rails and cut them to the final size on the final assembly.

I need a base and table to finish the skeleton of the unit before I start on the Y-Axis. I plan to use solid wood for the X-Axis table so I can level it on the first run. I am still going to use a Arduino with GRBL loaded up as the controller. I found a nifty Android app that can control the unit. It costs about $20.00 for the Bluetooth package I might use on the final setup so I can use a old Cellphone or Tablet as a dedicated unit. To power the whole thing I got a 19volt laptop power supply that is rated for 3.5 amps. Should be plenty. I can always add a 5volt regulator to power the Arduino.

CNC back off from the back burner.

Last week I was finally able to work outside again since the remodel for the exterior portion of my apartment building. I was rummaging around my storage closet and came across a sheet of Oriented strand board (OSB). OSB is dirt cheap, a 4ft X 8ft sheet can go for about $6.00 to $10.00 at Home Depot. I laid out by hand the parts for the frame of the CNC unit. Instead of having the Gantry moveable I decided to have the X axis move. I cleaned out the ruff lay out with my square and used the Jig saw to cut the parts out.



Since a Jig saw cuts ruff and like heck you’ll get anything squared up I used my hand router with a flush trim bit to make everything square and to the correct sizes.


As a reference for a straight edge I found a small piece of scrap wood that was square and used a hot glue gun to glue the straight edge to the OSB pieces.



After messing around with the Router I was able to get everything squared and perfect.


Nothing is fasten together yet. I will do that on the final assembly. I have found a few options for the spindle and a few ideas I want to try for the railing system. I plan to work on this more this Sunday.

Happy New Year and News

Happy New year to all of my Followers/Readers.

To roll out the New Year I have started a new job pre-wiring houses for TV, Data and Security. Some times even Speakers for Audio systems. It’s a easy job but the summer heat will probably suck.

Since taking on the new job we had to turn into a two car family. The Wife and I bought a 2016 KIA Forte since I turned the Family Van into a Utility work vehicle.

For the new Job I bought a RYOBI ONE+ Drill and Impact driver set from Home Depot that were on sale for 99 bucks. After using them for a couple days I have made up a little review performance wise. Lets start with the Drill. It feels nice and sturdy and some what light weight. For the work I do that requires to drill into multiple studs with a 3/8 twist bit it works fine but with Paddle bits it has no torque. As for the Impact driver it also feels sturdy and light weight. You can drive screws in like a hot knife thru butter. I was able to get by two days before having to recharge the batteries for both devices.

Yesterday I got a killer idea for a Cartoon. I got a hold of my oldest friend yesterday to talk about it since he does art and a few times we talked about doing a cartoon since I can do voices. I won’t go into detail about it but it will be a adult like cartoon comedy.

Old Point Of Sale Printer

A while back I got ahold of a Epson TM-88II. It’s a typical thermal receipt/ticket printer used with POS (Point of sale) systems. The printer I have has the RS-232 adapter. Sadly no power supply came with it but after digging around in my parts box I found a laptop charger that has the correct voltage and current rating. So I hardwired the power supply leads onto the printer’s motherboard after probing what was positive and ground.

The only PC I got running at the moment that has RS-232 is the junk system running Windows 98SE. The printer can’t natively work in Windows 98SE however since it is a serial device you can use the Generic text only driver.

To figure out what the serial port settings are on the printer you can hold down the FEED button while powering on the printer. This will print a short report of the printer settings and the serial port configuration.

For giggles I tried hyper terminal and connected to the printer. I can use it as a mini teletype system.

Just thought I was share my boring day.