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Friday, November 4, 2016

TwinTeeth Plus Build Log - Part 1


I want a PCB and I want it NOW!

      Have you ever had a burning need to design, layout then etch a 2 sided prototype PCB, at home, before you send it out to a PCB fab, to make sure everything is OK?
Well, so have I.

      I came across a PCB "design bundle" that I really want to try out and  build. 
This will be  the first in a line of blog entries, detailing my build process and review of this. 
Because of it's open source nature (nice one guys, thanks!) I had everything I needed to modify and adapt my design to fit the parts that I had. 
Therefore, along with these posts I will also upload the files for the parts that I redid, just in case someone happens to have some of the parts that I had.

...but first, some background on this

      I've spent a few weeks looking around for ideas on how to PROPERLY make a device that moves on 2 or 3 axes and  has a UV laser for a head. I wanted this to do a line-scan on a UV resin-coated PCB board, then etch it and have a prototype PCB done in  a matter of 30-60 minutes.
I quickly came to the conclusion that a  traditional gantry-style  CNC machine wouldn't cut it, in terms of speed.

      So, thinking about other stuff that has a scanning laser, I thought about how fast laser printers work. Then I began looking at trying to control a mirror array from an actual laser printer. 
In theory, it wouldn't be hard at all. Just have a hexagonal mirror spin on a spindle, shine a UV laser on it then pulse the laser so it will scan the board one line at a time. But, as always, the devil is in the details. 

      Suppose you have a PCB that's 10cm x 10cm. The laser position is fixed. All you're doing is generating a scanning pattern with the hexagonal mirror. That means, that relative to the center point of the PCB,  the laser beam will have to travel 5 cm in each direction (5 to the left and 5 to the right). This means that the beam length will be altered by ± 5 cm. 
According to physics, if the length of the beam changes, that means that the focusing of the beam will change also. 
What that means is, with a fixed focus, as would be the case in a scanning head, the beam will be focused in the middle of the board and it will be slightly out of focus on the edges of the board. If you have a laser beam that is not properly focused, it will leave behind an image that is blurry. 
And if you're doing  a board with, say, 0603 components on it, the pads will come out looking more like blobs of copper.

      Of course, laser printers have the same issue. The way THEY solve this is  they have  an  f-Theta lens in the beam path.
      For those of us that don't have Stephen Hawking  on speed-dial, an "f-Theta" lens  will take the incoming FOCUSED  beam of light and keep it focused, no matter the angle it's outputted at (or, put it another way, along the scanning path,  the beam, it will be focused in any point)


...Houston, we have a Problem!

      So, let's just Google "UV f-theta" lens and see what we'v....OH MY GOD!!!  How much?? F*** it! I'm taking up ballet lessons.

So, after I drank a cup of water, took a few Xanax pills and did that "Wax on wax off" move, I decided that I had to go back to the initial gantry style of CNC machine.

Note: for those curious enough to ask, a laser printer uses a RED laser. The PLASTIC f-Theta lens in a laser printer is NOT suited at all for the UV laser. The plastic the lens is made of  is not transparent to UV light.

...Long story short....

    So, eventually,  after searching the net for all kinds of ways to solve this, I found this site: and my jaw just dropped. Now, how about that... that was EXACTLY what I wanted to build.

But first thing's first: let me congratulate the guys (and gals?) over at for their hard work. Hope to see you in a Kickstarter campaign soon enough.
And no, I'm not in any way affiliated with them nor am I getting any money from them for writing this.
So, with the disclaimers out of the way, on with the story...
     I  began reading what these fellows did and how they hacked the Blu-ray laser head of the Toshiba drive. Of course, I contacted d the guys, and they recommended me the TwinTeeth variant of the PCB factory. The reason was that the original Mk1 design was kind of clunky and plagued with problems generated by vibrations.

Let's get building

      Now, I have to say, I really appreciate what these guys have done. They did everything from scratch, even developing their own hardware and software platform. 
And they've open sourced everything as well. To me, this is awesome, as everyone can get the files and make their own build, modifying it where possible and putting their own spin on things. So guys, a big  thumbs up from me!

I've decided on building the TwinTeeth Plus version, as this has less 3D printed parts and to me, looks to be more stable mechanical wise.

First off, I got me some 2 mm thick aluminium sheet (I couldn't find any 3mm plate)

On these, I glued (OK, scotch taped) the paper templates then marked where the holes would go.

After this, I went to print the 3 motor holders that the delta sits on. And here is where the real fun begins...
Looking through my collection of stepper motors, I happened to find 3 identical NEMA23 steppers. 

 The original TwinTeeth  needed NEMA17....Yes, this is one of the advantages of having a mechanical engineer for a girlfriend (Thank you!) She helped me modify the motor holder .STL file, so that it took the NEMA23 motors.

Next up were the bottom lead screw supports. Some F6900ZZ flanged bearings were supposed to be fitted into them. 
Because these bearings seemed to proliferate in the wild planes of eBay, but nowhere near my country and because I got burned by the national postal service (which sucks) too many times,I decided I would replace the flanged bearings for "normal" ones. (flanged bearing was d=10 mm, D=22 mm, 6 mm width; replacement bearing is d=10 mm, D=26 mm, 8 mm width)
 This meant firing up Solidworks and doing my magic. (I was stubborn enough that I wanted to do the part from scratch, by myself - what better way of learning Solidworks)

Unfortunately, the original dimensions in the .STL files have some wacky values, which proved to be a real pain to replicate. I had to build my own geometry on top of the .STL par to get the dimensions I needed. Then replicated and adapted that so  a 6000ZZ series bearing would fit.

Next, I got hold of some 20mm x 20mm square aluminium profile for the legs, 3x10mm, 200mm long  ACME (AKA trapezoidal) screws which I ordered to be milled on one end to 8mm, so it would fit in a 6.35mm x 8mm flexible coupling and  6 x 6mm, 300mm long guide rails, which I ordered to have M4 bolt holes drilled and tapped into them, at each end.

I also got some extra help for this build

He knows the vernier scale can be tough to read sometimes, so any help is welcomed.

Also, I know, the picture quality is really crappy.... I gotta get me one of those newfangled things called a camera. Tin-type photos, anyone?

Inches, millimeters, mills, centimeters....

      The only thing I found difficult about this project so far is modifying the existing parts. It's not that they're in .STL format.... it's the fact that the dimensions are kind of all over the shop.
At least, this is what I gather from measuring the provided .DWG files and the original .STL models. I mean, there are hardly any measurements that seem to have nice round values. I don't know if this is due to the fact that the design was done in inches, then converted to mm, or something else is going on, but it makes things kind of hard when it comes to taking measurements.

...come one, come all....

       This is the link to the GitHub page that contains the modified files. Like I said, I used NEMA23 steppers and  6000ZZ bearings and some of the 3D prints were modified for  MY specific build.
  As the build will continue, I will modify other parts as well. Why? Because it's interesting and because I have  an OCD about improving stuff.
Next will probably be the ACME nut for the 10 mm screws. I don't know if  a bough ACME nut will have more or less backlash than the original TwinTeeth method, where a mold of the screw was made and used as a nut, but those linear bearings held to the mount with  zip-ties...kinda make my skin crawl. 

Sunday, October 9, 2016

EF Johnson 242-5876 2-Way Radio Teardown

        Well, this teardown has been in the making for some time now. I'm not particularly big on RF stuff, but I had a hunch that this thing would be nicely engineered and built on the inside. I was expecting a lot of analog goodness mixed with some digital control.
And what do you know.....I was right.


      Now, I've searched high and low for a manual to this thing, but I wasn't able to find anything. And when I say "anything" I mean absolutely nothing relating to that model number, which kind of lead me to believe that these things (of which I have two in my possession) might be a custom  police or military issue (police most likely).

     If anyone has a user manual, or better yet, a service manual, please leave a comment. I'd really like to see how this thing ticks.

Most of the hand-held stuff I came across from EF Johnson seems to be operating on the 800-900 MHz range, but this thing  seems to work on the 80-100 MHz range. I did a quick FFT on my Rigol 1054 and there seems to be a nice big spike at about 88 MHz when I press the transmit button. Also, the FM receiver chip is spec'd for up to 200 MHz.

However, this should be taken with a grain of salt, because these things require a network infrastructure to work. So without that network, I can't say for sure that that spike I see isn't just a signalling band or something.

Ok, enough talk. Let's get into the meat of it.


This thing is ancient. How I know this? It uses Ni-Cd Batteries. 7.5V, 1.4 Ah. And yes, they still take a charge, but that might be because at some point in time someone sawed off the back of the battery pack and stuck new batteries in it.


Taking the back off, you can immediately see this thing resembles something that's MIL-spec. A nice thin cast magnesium (probably) shielding with a ton of screws.


Lifting up  the skirt, this thing really looks packed full of parts. (Yes, I know, I have to get a better camera.)
The two 14 pin chips are a Motorola MC14066B Quad Analog Switch (the one on the left) and a MC14094B 8 stage shift register with 3-state outputs.
The smaller 8 pin one is an MC939  divide by 6 counter (I think...)


The face together with the keypad came right off, revealing another shield, also cast magnesium, together with a boatload of adjustment pots and caps.


On the back of the face, there are two boards stacked together and which connect to the rest of the unit only through that pin header. Also, notice the nice o-ring  seal (OK, not really O-shaped, but you get the picture). A bit of it is peaking out in the lower left corner.
There are a few goodies on these boards, but let's leave it to the side for now and take a look at what;s under that other shield.


Et Voila! This is the good stuff. A whole myriad of analog and digital goodness, just waiting to be reverse-engineered. Not by me, mind you. I'm not into this kind of stuff, remember?
And, because I have a shitty camera, I tried to make things easier, hence the red markings.
So. from the top left corner, we have the MC3362DW  FM receiver chip. Now the datasheet says it works up to 200 MHz, and this is consistent with what I saw on my scope's FFT.

On the right, we have the MC145158-2 which is a serial input PLL sinthesizer.  The two  PCF8574  probably shift data to and from the two vertical boards. Unfortunately, I couldn't read the part numbers  off the ICs because there was no angle I found that allowed me to do so.

What I plan to do  is if and when I get a hold of some manuals for this specific model, I'll  do another teardown sometime and desolder these 2 boards and have a proper look at what's happening in here. Also, I want to poke around some stuff in there with the ol' 1054 scope. Some LO's, some I2C buses... stuff like that. Who knows, maybe I'll even get to learn more about the RF side of things.

Ok, so now let's get back to the boards on the faceplate.


     So, first thing to notice is the big chip to the left of the speaker. That's the PCF8576T driving the LCD on the front. And, of course, it's controlled via I2C. To the left of that, there is a keyboard  controller, the MM74C923. It can encode up to 20 keys, which is  5 more than what the faceplate has. "What a waste" I hear you say?
Well, yeah, but being the smart engineers that they are, they probably read the datasheet and it looks like if you're decoding a 5 by 4 button matrix, then the 923 is the way to go.

Here's a funny thought....maybe a Rigol engineer will somehow make his/her (everybody deserves to be an engineer) way to this blog and decide to turn over a new leaf and actually start reading some datasheets. They're free to download, people... just so you know.
OK, rant over.

Just above the 923 controller, there's a 14-pin X24C16  16Kbit (2048x8) EEPROM, with an I2C interface, as one would expect. Chalking this one also on the list to probe, for the next teardown.

Now, going to the other board, we have the big chip to the left. It's made by Motorola, just like  most of the other chips in these units, except my Google-Fu can't come up with a part number. Most likely it's a custom part...hence the label on it.

Also, the buttons on the side  seem to match the ruggedness of the unit. Despite how mucky the bottom transmit button looks, it's still got some life in long as you press it juuust right. It's one of those Goldylocks things. not too hard, not too light of a press....

And, after putting it all together again, what do you know....It still works

All in all. I'm pretty impressed how this thing was built. You gotta love the good ol' days. 
If and when I get hold of some more information about this radio, Ill try and play around with it a bit more, maybe even connect it up to a PC and see if I can modify something in the firmware. 

This link has some info on how the remote interface cable and about the PC software.

I'm also going to do a mini-teardown of the charger, just to see what's in there. I have 2 kinds of chargers: one that plugs in directly into an AC outlet and another that takes in 18 V DC, so stay tuned for that as well.

Full teardown pictures are available on my Picasa Google Photos page.

Thursday, January 14, 2016

Picoscope 3000 Series Review....or maybe not

  First off, let me start by saying that this is not really  a full review, but more accurately a first impression after I got to play around with one of these things. 
And because it's a PC scope, the impressions are not so much about the physical aspect of the scope as it is about it's user interface. And, boy, do I have some comments to make here...

"High Performance USB Bla bla bla...."

  The culprit....sorry, I mean the product I had the... opportunity? to play with is a Picoscope 3406D MSO PC oscilloscope.
This little thriller comes with 4 analog channels and 16 digital channels, a 1 GS/s real time sampling (even though the software lets you select all the way up to 2GS/s, but I don't know if that really does anything or it's there just for  the fun of it), USB 3.0 and more features than you can poke a stick at.
Yeah, right. 
And let me make an analogy here: suppose you go to the  local car dealership and go around the show floor, only looking at the specs where it says "Horsepower", paying absolutely no attention to, let's say, how comfortable the interior of the car is, or how well it drives on the street, or... I think you get the point. 
When you do find the one with the most horsepower, you give the dealer all you hard earned money, two small coins, a bottle cap and a paperclip you happen to have in your pocket, making sure you quickly but the latter two back in you pocket, as fast as discretely as possible.
After  you drive home, happy about you new purchase, you will be hit by the worse case of buyer's remorse, ever, because, you will have realized that you just bought the most ugly, uncomfortable, unusable car in history. See where I'm going with this?

So, yes, the hardware specs for the Picoscope 3000 series are very nice, and maybe the scope would deliver on them.....who knows... because I was too preoccupied with getting the software interface of  this thing to actually  work and with scouring through the menus to find basic stuff  like a cursor,  getting the waveforms to actually fit in the center of the screen, and so on. And for these kinds of scope, where all you have is the interface to it, no buttons or knobs, how it looks and feels makes all the difference.

Yes folks, it's bad. The Picoscope software interface is horrific. In the year 2016, when more and more really nice PC scopes are coming on the market, the interface is really frustrating and awkward to use. This, combined with the fact that it looks like something from 10 years ago, really makes you wonder why on earth someone would go and buy this product, as opposed to any other scope of the same caliber. 
First of all, when you start the application, as a first time user you will be met by the most mild-mannered and spartan GUI yet. Also, notice the selected 2 GS/s rate. YEAH baby, now we're talking 

At first glance, you'll notice that it has all the things a normal scope should time-base and Volts/div settings...and trigger settings. Sweet!

On to the fun stuff

Now, for any engineer that has ever used a scope for more than 5 minutes, you will soon realize that for some measurements, you need some way to measure the time interval between event A and event B in time. Nothing more simple, just press the "Cursor" button an a scope's front end.
Well, this detail seems to have escaped the guys that designed this interface. After a frustrating hour of searching all the menus, all the nooks and crannies this interface has and calling another one of my colleagues to the rescue, nu luck. No "Cursor" tab, or menu, or anything like that. Only a daft looking green  little circle tucked away in the lower right corner, that has the amazing property of displaying "0°" on it, no matter where you move it on the waveform.

Again, this is from the perspective of a first time user. It shouldn't be rocket science to use one of these devices and I do apologize if some people that have read the user manual for the GUI know where everything is, that still does not make it any easier to operate.

This thing is also boasting all kind of communication protocols decoding, which is very handy. Except that, with 4 analog channels and 6 digital lines, all 6 with CAN protocol decoding on them, the GUI gets sluggish sometimes. And that happened on a i7 core machine with about 8 Gigs of RAM on it.
Also, that "real time sampling" the scenario I used it, no way was that real time. But who am I to complain.
Also, there was a very peculiar thing I stumbled upon....the traces would not zero properly, i.e. they had a a butt load of offset, one of them about 100 V. But, the guys from Picoscope thought of this ahead, and put in an auto-zeroing button for each channel

Too bad each time I zeroed channels B, C or D, the application crashed.
 A nice thing is that this thing always has the last 32 frames on hand, so you can review them  at any time, to see any missed signal behavior (see the "32 of 32" in the upper middle of the photo). Nice feature this is. But unfortunately, from all the button pushing, my application decided to go all Alzheimer on me and by the time I managed to set up my signal capture profile, both analog and digital (it only took abut 2 or 3 hours, what would have taken me 1 minute on any other mixed signal scope), the GUI only had the current frame on memory, and nowhere could I find something referring to the buffer size or history or the like. So, yeah, all we had to go on was a trigger on a certain event an hoped that all went well.

The Bottom Line

If this software was a pre-beta, OK, I would excuse a few mistakes in the code, here and there. But it's not. The version I downloaded was the latest one. It even said "stable" in the comments next to the version name, in Picoscope's Downloads page, so it had to be good. (F.Y.I. This version also crashed when I hit the "Zero" button for channels B C or D)

 I wonder why the latest version didn't work......

Anyway, a LOT of improvement is necessary here. The guys at Picoscope need to step up their game and actually build a GUI that works. I'll even lend them my scope and see how that works, since obviously none of them ever touched a scope before, otherwise they would have known to put all the common and important stuff where it can easily be accessed, front and center.

So, what's next?

Well, I've been doing a lot of work an my own personal projects lately, and built some nice gear. Of course I'm going to share them, pictures, schematics and all. Also, there's some power supply stuff going on that I want to share.

Also, I've been thinking about building my own LCR meter. After reading and doing some hard core research on the matter, I came up with a configuration  that I hope will work.

So, more interesting design posts to come.

Have fun and keep playing

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