This calculator has an ALPS plotter mechanism. The original pens aren't available any more, but you can buy some expensive new ones of a slightly different design. Or you can attempt to make a pen out of a holder and a chopped down ballpoint refill.
From some brass rod I machined a holder which is the same shape as the pen, with a hole at the front which will hold a ballpoint refill.
It fits in the plotter:
The refill used turns out to be critical to the functioning of the pen replacement. If the tip is too wide then it simply won't fit through the hole in the sheet spring in front of the pen holder. If it's too small then it has no spring action. The first refills were too big, the second set (0.5mm I think) were a bit small but worked.
The holder jams now and again, but does write successfully.
I now have quite a few instruments for electronics, some scopes a logic analyser and a thurlby multimeter/serial analyser/scope. the end of the workbench now has a gap after the shelves were built, and I was going to fill it in with a piece of worktop. Then I measured the instruments and found that they all fit in the gap. So, after a quick bit of wood bashing:
I have used some scrap wood and old flooring and made a simple rack for the equipment:
The rack is on wheels so can be moved about. I am hoping that the space freed up on the workbench will be more than I would have gained by filling the gap where the rack sits with more worktop. I think it will as I can have the logic analyser and scope next to something I'm working on and take up no bench space. We'll see.
As it's made of scrap wood, I could just dismantle it if it doesn't work out.
One circuit of a pod and some routing and we have a pod for the LA4800:
It's a bit big as I just wanted to see if the circuit was correct and I anticipated lots of scoping. As it turned out the only problem was the transistor pinouts and the orientation of the pod cable sockets. Neither of which is much of a problem. as the pod works.
Here's a quick trace of some signals on the Epson HX-20 IO port.
The analyser works perfectly as far as I can see, apart from the display problems, which really are a shame.
I had to solder wires on for this test as the clips I ordered haven't arrived yet, but that's fine.
One of the nice things about older hardware is that a lot of it comes with expansion connectors or other ports that allow you to attach arbitrary hardware to it. The HX-20 is no exception and comes with an expansion port which allows access to the bus signals of the main processor (yes it has two - almost dual core). I wanted a simple IO port so breadboarded a simple 8 bit output latch and 8 bit input circuit using old fashioned 74 series logic.
As a more permanent solution I routed a PCB.
I then used an old PC HDD cable to attach to the HX20 which helpfully uses a standard 0.1" pitch IDC connector. Unhelpfully they have used a different numbering scheme to the rest of the world which means the pin numbers are all jumbled, but that's not and unsolvable problem, just an irritation.
The output port can be used to drive other hardware, I'm going to use this one to drive a relay module:
The bottom two bits of the data bus are wired up on this PCB, so you write to address &H5000 and D0 and D1 will end up latched in the output port. To read inputs you read the same memory location, again D0 and D1 are the data bits that are wired up.
When I needed to look at waveforms on a digital interface recently, I used my Rigol scope as a logic analyser. It's not a mixed signal scope, but it has some features that allow it to be a 4 channel logic analyser. It can decode a parallel 4 bit bus as hex, for instance. It was right at the limit of what it can do, but as a logic analyser it was really at the bottom end of what I wanted it to do. So I looked about for logic analysers. There's a lot of the HP analysers about but they tend to need software on floppy disks and they will be decaying and get harder to find as time goes by, and they are mechanical and that is always the first thing to go.
Then I saw the Thurby Thandar (or TTi as they are now) LA4800 logic analyser.
It has it's firmware in ROM, and has 48 channels. It can go to 100MHz, but runs slower with normal pods. As an added bonus the service manual is on the internet, which makes it fixable.
I saw one on ebay and bought it, unfortunately without any pods. This isn't a massive problem as the service manual has the pod schematics, so I'm having a go at making a pod for it. Just a simple 32 channel pod, we'll see how it goes.
The analyser suffered a bit in transit and the display has a couple of odd faults on it, which is a real shame, maybe I'll find another one as a spares machine? Anyway it didn't start up when it arrived either, but it looks like it had a drop on the way here and the display connector had moved a bit, as after unplugging and replacing the display connector it works.
This one was iconic back in it's time. It's still a nice small BASIC pocket computer, but the initial problem I had with it was the batteries. It uses 1.35V mercury cells originally, and they aren't available any more as mercury is very naughty.
Most modern button cells are alkaline and generate 1.5V, so putting four of those in this machine would result in 6V, which is quite a bit higher than the 5.4V that the mercury cells would have generated. It's probably going to cause a failure as such a higher voltage. Fortunately, if you add a diode in series with the batteries you can get 5.4V from 6V as 0.6V is the standard diode forward voltage drop. I also have a service manual for this machine and looking at the circuit diagram it looks like there's no centre tap taken from the batteries, so the lower voltage should work.
I soldered a diode in to the machine, which was easy as there's plenty of room available:
The new diode is the one to the right of the diode with the yellow stripe on it. It's a bog standard 1N4148 I had in stock. After fitting some LR44 batteries, the PC1211 started up:
Jolly good news. I'll see how happy it in in the long term.
The printer is a different story and for now hasn't sprung into life. There's an internal battery pack which looks remarkably well considering it's age, so I'll try recharging that for a while. If that fails, then I'll swap the batteries for new ones.
I recently bought one of these calculators as it is a calculator of a type I didn't know existed until recently. It is a simple non-programmable with the added feature of a small ALPS four colour pen plotter. It can print out bargraphs, pie charts and tables of data that you enter into the calculator. I knew the ALPS mechanism was used by many manufacturers and many years ago I had a printer that used the mechanism.
It's a well known problem with these printers that a couple of small gears split with age and the mechanism dies. Unfortunately this had happened to the mechanism in my calculator as well. This stops the pen carriage from moving left and right and also the paper from feeding.
Some people have successfully fixed their mechanisms using small gears they have bought and others have 3D printed replacements. I thought of that but then I have a workshop for making things, so maybe I'll have a go at making some gears. I ordered some 4mm rod in various materials and went to set up the CNC 3020 ready to machine gears. Unfortunately the computer that drives it failed to boot properly and as a double whammy the spindle PSU has failed.
So, I decided to set up on the mill and do the gear cutting manually. I used the rotary table:
The cutter is a 0.2mm D bit that is one of the cutters I use on the 3020 for PCB milling. There's 13 teeth on the wheel, it has a 4mm OD and a 1.4mm hole for a push fit on the motor spindle. I worked out the 13 angles needed and cut a gear to a depth of 0.4mm or so. The dimensions are a bit rough as it's tricky measuring exact sizes with the manual calipers I have. I could use the spindle camera I suppose...
Anyway the gear was cut and I drilled a hole (1.2mm but enlarged manually, I had no 1.4mm drills, surprisingly as I have lots of drills of different sizes).
I managed to get the gear onto the carriage motor and it seemed to work, so I cut the second gear for the paper feed. Trying it out the papaer feed gear just didn't turn freely. I gave up and cut another one, this second one was much better:
I'll maybe cut it down to size later, it seems to work fine with the extra length, so I'll leave it for now. The carriage gear is here:
There's some oil from the mill on the wheel, it's actually white acetal.
The mechanism runs well enough to print out pretty well, here's the printer test (only two pens are working, I'll have to get some more somehow).
So the calculator now prints almost perfectly ( the carriage seems a bit too loose and rotates as it is drawing, not sure what th eproblem is there), and it's just as mesmerising as the plotter I had way back.
One problem that is left is that the LCD display has bad bleeding:
I have an ambitious possible solution for this, but it'll take a while to get to it I think.
The electronics room was a bit untidy so I ripped out the shelves I made from old pallets and made some new ones from scaffolding boards. These shelves are very strong, I was sitting and standing on them and they didn't bend more than a couple of millimetres.
More tidying needed, but they make much better use of the space, especially with the IKEA boxes. They don't smell bad like the old pallets did, either. Turns out it was the legs of the shelves I made that were smelly. They came form the old garage roof and were some odd type of pine that probably didn't play well with the moisture in the garage.
Up until now I have been using self adhesive crushed velvet paper for soft linings on pen boxes. This has been OK, but I spotted someone using some flocking on a YouTube video. It looked interesting so I decided to do a test.
I made up a 'box' which had two flocked surfaces on the inside.
The surfaces are glued then flock fibres are 'puffed' onto it with a puffer bottle. It works well, but does give a different, harder surface that the crushed velvet.
The real advantage is when you come to coat one of the pen slots that I mill into the boxes to hold pens. This is really fiddly to cover with paper. With the flocking it is easier, but you still have to be careful to apply glue in all directions and then ensure the flocking is uniformly applied to avoid gaps. As the glue is the same colour as the flocking it's not a total disaster if the flocking has a small gap here and there.
This is a trial pen slot that has been flocked to see how well it works. Apart from a small gap it worked well. There's maybe not as much cushioning to protect a pen as the self adhesive paper, but it's definitely better than just a wooden slot.
I need to tidy up my dust extraction and the first thing to do is to put the extractor somewhere closer to the ceiling where I intend to run extraction pipes to the machines that need it. So, the first use of the new scaffolding boards. We have a shelf:
I now need to get some new filters for the extractor as I'm nearly out of them.
The first chair that was made of scaffolding boards didn't work well at all, so I made another one. That looks to be much more successful, so I needed to get some more scaffolding boards in anticipation of making more chairs. I tried to get more at the salvage place I got the first boards but they only deliver a minimum quantity of 200, which is too many in one go for me.
So I had a look around and found a place in Havant called Total Scaffolding. They were great to deal with and had a minimum quantity of 50 boards. That's still quite a lot, but manageable. So, the day after visiting them they arrived.
That's a set of chairs and several other things being craned into the garden. I then stored them in the garage.
The chair has a temporary covering now and some foam. The thickness of foam was tested and about an inch seems to be the best thickness.
The covering is a smaller piece of fabric than is necessary, but it's just a scrap piece so I added another to give an overall covering.
The height adjustment has so far resulted in a 10mm reduction in height which had a large effect on the feel of the chair. It looks like even a few mm makes quite a big difference to the feel of the chair. <Maybe I should have measured the chairs we looked at a bit more accurately...
There's been some movement on the chair project. I have used the CNC3020 to make joints, which makes a very neat joint and parts that are more or less interchangeable.
Both mortices and tenons are done with custom gcode programs. I have finished all the parts for the first (trial) chair and have glued it up.
The chair is pretty solid so far, the seat needs fixing now and some covering with fabric. Some foam is also needed as these won't be wooden seats, the thickness of the foam needs to be determined.
The seat blocks were originally going to be wooden, but with the 4 degree sides and three screw holes, I have decided to 3d print them.
They really are much neater and are very strong. Also, I get to do something else while they are being printed (I can probably print a chair set at a time if it'll fit on the print bed) and I can have almost any colour I want.
The breadboarded ARM DRO can finally get the TFT display to display something over the SPI interface. I've used the same x*y colour map:
This is good news as it's a movement forwards. It turns out that I wired the JTAG signals to some of the TFT interface signals and the JTAG was turned on by default. As I want to keep the JTAG debug facilities I'm going to rewire the interface on the PCB. I will mill another PCB at some time, so it doesn't matter too much.
I now need to get the touch screen controller talking, then all the hardware will be talking. Then on to make some more complex firmware to do DRO type stuff.
I've done some more joints on the CNC machine. Here's one at a fairly accurate 4 degrees:
This is for the seat of the chair. It's a pretty accurate 4 degrees, set up using wedges that I 3D printed at various angles. This is the joint being machined. It's a fairly simple tool path but fairly efficient. It takes about 25 minutes for a tenon (mortices are quicker), but that time isn't dead time, I can do something else while the machine is working.
I've mounted the ARM based DRO on the wall and attached two gauges to the lathe. The Y axis isn't attached and the code mirrors the X axis, but apart from that it's working:
The gauges are here:
I've re-cased one PCB but left the other one with a display. I'm not sure what I'll do with the next ones, it depends on the space I have available. There's only two channels of gauge decoders plugged in at the moment, both decode the cheap Chinese gauge data streams (24 bit). For some reason I've not worked out I have a signal problem with the channel that attaches to the more expensive gauge that outputs the 2x24bit data stream. I need to build some more gauge channels and attach gauges to the mill and the third gauge to the lathe.
The TFT display isn't working at the moment, I have to get the SPI protocol working, I'm going to do that on a breadboard.
I'm going to try the DRO out as it is for a while and see how it goes.
These are some more mortices and tenon test pieces. They fit nicely but I think there's enough room for glue.
I now need to make some angle plates so I can machine these at the angles I need for the chairs.
I think you could make the tenons and mortices different shapes if required, which is an interesting option where multiple joints want to be in the same space, such as where two rails attach to the same upright.
I've got gauges working again on the DRO, currently two of the cheap Chinese calipers using the 24 bit data output have run on two axes of the ARM based DRO. There's a few minor PCB errors but nothing major. The switches should work soon. The only major part not working is the TFT display and that could be a code problem, or a non functional display. I've switched to an SPI TFT display, and I only had a non touchscreen version. I'm waiting for the touchscreen ones to arrive. Based on the parallel display experience, I think about 50% of these displays don't work out of the box and of the remaining 50% only half have the advertised display controller chip on them, the other half have whatever chip was hanging around when the displays were built.
Here's the ARM DRO with a channel working:
The daughter board is plugged in at the bottom left. That has a PIC 12F1822 on it that converts the data form the gauge into I2C which the main board polls in its idle loop. There's room for five more boards across the bottom of the main board. As you can see the gauge reading is on the Z axis in this picture.
I've had two 24 bit gauges working, the third one I had wired was of the 2 x 24 bit packet format, which did work in the past but failed for some reason when I tried it. I'll make some more daughter boards and debug the problem..
The more expensive gauges I got as a trial are ironically less stable when powered off the DRO 1V5 supply so I may move to cheap Chinese gauges as they are also 0.01mm resolution and seem more tolerant to my 1V5 supply.
With regard to the DRO PCB anyway, just this time it is using an ARM (LPC11U14 specifically) on an LCPXpresso board that I had floating round for another project.
As you can see, the code is ported over, well the OLED driving stuff anyway, and all is up and running. Just the TFT and LED displays to do, then I can attach the gauge boards and get it running. That's where it all started to go wrong with the PIC based PCB. The LPC stuff is much more solid. I've not seen the OLED problems I saw with the PIC, and it's the same code, so there was something odd going on with the PIC. The LPCXpresso board has a JTAG debugger on one end too, so the DRO has it's own debugger. That works perfectly too, I've managed to get a stack trace from it when I made porting error, and it was easily debuggable. All in all, much better.
The only thing is that the LPCXpresso board is much more expensive than a PIC chip, but I can probably make my own target board later and take the LPCXpresso board off the DRO. Maybe. I may just leave it there, it'll make programming easier later on.
I need to do a lot of mortice and tenon joints if I'm going to do the chair project, and they aren't fun and never look very good in pine, as it's difficult to work with. So can you do them on the CNC3020?
Well, after 3d printing a clamping plate that attaches to the 4th axis mounting bolts on the front of the 3020, it turns out you can do some very consistent nice looking tenons and matching mortices:
These are test pieces, but they are very consistent, totally interchangeable and look nice. The clamping bracket lets me put tenons on the end of long pieces of wood, I 3d printed it and it's strong enough to hold the work.
In order to get the spindle out in front of the bed of the CNC enough to do the entire tenon, I had to make a spindle extender attachment. I did this in wood as the 3d print was 6 hours or so, I may do a 3d printed one later if I use it much.
This gives me enough extra over the end of the machine to do the work I need for the chairs. I'm a bit concerned that there may be heat build up due to the insulating properties of wood as opposed to the aluminium heatsink arrangement the spindle normally has.
Of course, this is also going to be true if I 3D print a version. I may have a think about a 3d printed cylinder in the existing heatsink and an aluminium clamp attached to it that gives similar heatsinking as the current clamp. I don't think the machining will take too long so I won't be running for extended periods of time, but it may be better anyway.
Perhaps a 3D printed version with holes for ventilation?