New Arrival 11. - kind of...

New Old arrival.

The things I picked up today are not new, not even for me.

A friend started a community lab a few years ago. I donated to him a bunch of test equipment. Actually I had a much smaller lab myself, and I over collected things.

Then came the COVID. This killed the the lab. 

My friend finally gave up, repurposed the lab, for his own purposes.

Most of the equipment I gave, has not too much use for him. He felt, that it wouldn't be appropriate, to give away those things. So we agreed, that the equipment he doesn't need, or used come back to me.

Today I went to the lab, and picked those up.

Bunch of FreeScale (now NXP) development boards, a CubieBoard, two BeagleBones, and a big Analog Devices Backfin development kit.

Also some nice test equipment:

Fluke 8500 multimeter, a Fluke/Philips PM3082 Oscilloscope (Even, I have a second one from this), a Tektronix 1240 and a 1241 logic analyzer.

For the logic analyzers I even have the original carrying case for the probes (with full of probes).

My plan is to switch on, test, and sell most of the things above, as I barely need them (may keep, some of it, but this is not the main plan)

VU Tower

I have children (a boy and two girls).

I always have in mind to connect my hobbies to my family. It not always turns the way I'd like, but not this time. For precious moments time-to-time I make presents myself. Like the repurposed radio for my mother for Christmas.

During the last weekend was one of my daughter's 14th birthday. She is moving to party age soon. What would be better than something with lights connected to music.

This project is just a simple, floor standing VU meter, using a microphone board, Arduino Nano, and WS2812 LED strip. Quite a simple one.

I had issues with the microphone board. I bought all together 7 different kind. It would be a long story the troubles I had with those (so not writing it today). Finally I choose one from DFRobot. Mainly because the two 3mm mounting holes, what perfectly fit into my design.

I don't want to write to much about it, so the pictures.

The finished "product" (first, just because it looks better when sharing on social media. 😂)

Bare electronics:

Assembled without the full enclosure:

How it is work (It is just her sisters yelling. I'm afraid, if I use some music on it, one of the YouTube's piracy dickheads ban it). It also has yellow and red, but unfortunately can't be seen on the video:

All of the elements (mainly code and the 3D design) can be found in this git repo. It also contains other VU meter related things, what is "work in progress" and not connected to this project:

https://gitlab.com/suf/suf-electronics-vu-meter

New Arrival 10. - Additions to my lab

There are many other things arrived since the last "new arrival" post, but today, I'd like to focus on the additions to my lab.

Agilent 53131A

Actually a few years ago I bought a 53181A Frequency Counter. Actually one of my former projects required a two channel counter, so it was itching in me, to get the bigger one.

For surprise my old 53181A had the high stability oven option. So now, I moved the OCXO reference to the new unit. I'll sell the 53181A finally (no, don't ask for the price, I've the buyer for it).

I finished the project were I think before, I need the analog multimeter, during the weekend - without it. Before that I scored this nice Hioki FET multimeter.

I don't know, if or when will I need it, but for ~$40 is nice addition to my lab (actually building some bench unit is still in my focus)

I still have one half junk PM3082 oscilloscope lying around. I didn't give up to repair it. There is no picture on the CRT. My suspect is the high voltage supply. Playing with the 16500V rail is not a child play.

I scored this for nuts, to achive the task (when I have time for it):

Fluke 80K-40 probe in carrying case. Good for 40kV.

Two additional equipment. Those are not yet arrived. Those are somewhere at the currier services

Bruster Digistant 6405

Yes, I have already a similar unit, but for GBP60, I can't leave it there.

Boonton 8201 Modulation Analyzer

No, I will not become an RF guy. Actually I've four Panasonic/Leaver VP-8193 units. I want to test, repair them (and finally sell three of it).

I read through the service manual. I have most of the required or similar test equipment mentioned in the manual (Audio Analyzer, Oscilloscope, Low frequency spectrum analyzer, multimeters, etc.)

The only missing piece was the Modulation Analyzer/Measuring Receiver. The manual mention HP 8901A/B or 8902A. Those units are going for insane price on the eBay.

I was thinking to try to simulate the function with my HackRF SDR, but I think the result will be questionable, and probably need some programming, what is time.

I was so fortunate to score this unit for the third of the cheapest HP 8901A. I think this one has the same, or better function, and optically looks much better, than any HP unit I seen online.

Analog Multimeter 1.

I restarted to work with electronics around 15 years ago.

At the beginning I decided, not to use analog meters (except on audio amplifiers) anymore. Those are not precise, outdated, etc.

But the things are changing.

I started to working on a project, what done some weird things. I guess, with changing the load, the power voltage is dropping and disrupting the input measurement.

This is something, I will never see on a regular digital multimeter. I either can use some higher speed data acquisition and record the result on a graph, or use an analog multimeter and see the needle movement.

Actually I don't have none of the methods actively setup at my lab.

I decided to go to the easier way, and get an analog multimeter working. 

I still have an old Russian meter from the soviet era, inherited from my grandfather (he were the person teaching me electronics, when I was six). This meter was lying on the ceiling, as I didn't use it.

This meter wasn't switch on let say 30+ years.

This can be seen on the batteries left in it:

At least, those doesn't cause to much damage. Just some minor corrosion.

Anyway. Those meters only use batteries for resistance measurement. For this, I'll definitely will use my digital meters. So no batteries going back to the case.

Opened it. Actually it had the original factory seal on one of the screws. It was never opened before.

It is in perfect condition internally.

Tested. It is spot on. So I'll keep it for my measurements, where analog has advantages.

This could be the end of the story. But as usual, the little devil in my mind started to chase something.

I like much more the bench instruments than the handheld ones.

Looked around on the eBay. But didn't find any subject with reasonable price and condition.

What would be the result, if I design something, with the current component possibilities.

I have quite a few Ganz 101DA-2 panel meter. I bought a few as new, a few others on a ham market.

Based on those meters, I may can produce something interesting.

First, I started to work with one of the panel meters.

These things are by design has 100uA full range. The ones I bought has internal shunts to 5 or 20mA. First I wanted to remove those.

Last time I was playing with those units, I was a bit rude. Directly measured the resistance of the coil, what is definitely not a good idea (https://pakahuszar.blogspot.com/2022/09/analog-meter-resistor-sizing.html).

This time I was much more careful.

Used my Digistant voltage standard as source (it is not calibrated, and a bit off, but it is perfect for a very low voltage source), a current and a voltage meter.

So the result for the full scale is 95uA and 22.22mV. This means two things to me:

The coil resistance is ~234 ohm, and I can drive meter to full scale with let say 25mV. So I can play with these values.

With a good low noise FET input opamp, I may can go down to uV range while keeping high input impedance (thinking about 100Mohm).

We will see the results.

As you see the original scale plate is white, with just the start and the end marks. It is made from 0.9mm aluminum. I need a scale, but I have no equipment to make it from aluminum and paint is accordingly.

In addition, it would be nice to have a mirror scale (why not, if you can).

The original case, even have place for the mirror

I was thinking to find a place, where somebody can cut the proper mirror to me with waterjet. Thinking it further, I decided, to design the mirror size, print it in 3D and use a self adhesive mirror foil on it.

Next is the scale itself. I was thinking, how can I create the scale. First printing on paper and laminating it was my idea. But this is not the best for the mirror scale, as the cutout would not be easily achievable.

Then came the idea. What if I design it in KiCAD and send it to a board house for manufacturing.

So the design born. The scale was designed in OpenSCAD, exported to DXF and used by KiCAD.

Here is the result:

As the board house create minimum 5 pcs, I'd like to figure out, what design to put to the other side. Then I'll send to manufacturing.

This is for now. I'll continue, as my build advance...

VFD Mania 2. - Inverting boost converter

For the -27V supply I mentioned in the first part of the series (https://pakahuszar.blogspot.com/2023/02/vfd-mania-1-preface.html), I wanted to have something cheap, and from easily available parts.

Yes I know, that the MC34063 is old, not to effective, but still widely available, has calculator, tons of circuit configuration in the datasheet, and extremely cheap.

As I wanted to create -27V from the 5V supply (I want to run the module on the way, to have only a single supply input), I decided to have an additional external transistor, as even with 100mA output, the switching current on the internal transistor would be over 1.5A, what is the maximum of it.

The required circuit configuration is on the datasheet (choose the NPN external switch version), so I just used it in my design.

Ordered the panel, arrived, and built it.

PIC

On first switch on, no output, just some smoke. 😕

It happened, let say 6 month ago. I put the whole project aside as I had many more things to do.

A few days ago it started "itching", to do something with it.

Actually, I looked for other possible solutions than the MC34063 (found some, but the component availability is still an issue)

Then I revisited the datasheet, and the original schematic, to figure out, what is the problem.

Redrawn it a bit different form, and realized something.

The R4 in the schematic above (according to my understanding) has the role, to switch of the transistor, compensate the base capacitance (it is low, but still exists). Then I realized, it will not fulfill its role. When the inductor voltage fall below -0.6-0.7V, it switch the transistor back on. The R4 should be between the base and emitter instead of the base and the ground if even needed.

I just removed it, and the circuit started to work perfectly.

It draw ~200mA from the 5V supply without load. Not good, but acceptable:

Checked, in the datasheet, if I was the idiot, when designed it.

It looks like not. The design flaw is coming from the datasheet.

Finally, I wanted to see the supply noise. I seen some weird waveforms, at ~22.5kHz, what is not the expected switching frequency. (First real use of my shiny new Rigol MSO5074 oscilloscope)

Then it pop into my mind, what is the input the supply gets.

Oh, my! The yellow is the output of the newly built converter, the blue is the output of the used Axiomet bench PSU. Ok, I realized, why to use linear bench PSU (or maybe a good trusted switching one) when it come to noise measurement.

I'm planning to do that measurement later on.

Next part is planned on the filament supply.

To be continue...

VFD Mania 1. - Preface

I'm kind of maniac, if it comes to the VFD displays. I've several instruments in my lab with VFD.

Even I collected many various versions with the thought, once I'll build something from it. Actually my first acquisitions were VFD modules, what already have all of the power supplies, so I not need to know, how to power, how to drive them.

On the other side, I always wanted to know, how VFD displays are working, how they need to be driven.

This story begins 8 month ago, just the half written article was put asside.

Then I seen this nice bare VFD so cheep, I couldn't resist. Bought them and my learning journey begins.

Now, I already know, it works like the vacuum tube.

It needs some heating voltage for the cathode, need anode voltage, and it have a grid to control the electron flow from the cathode to the anode.

In addition it has direct heating, so the cathode and the heating connected together (here it called filament supply). It is somewhere around 2.5V and recommended to use AC voltage (few 10th of kHz) to achieve even light distribution from one end to the other (the heater strings are connected to the two end of the VFD tube). For the anode/grid you need a voltage around 30V (it can change from tube to tube). With this one I was fortunate to figure out the original equipment this VFD was installed, got a service manual. It looks like it needed 32V.

On the side of the power supplies I need some IC, designed for driving VFD.

I choose PT6324 from Princeton Technology.

It is cheap and easily available from the eBay. Also it able to drive all of the segments of this display.

There is not uncommon, but for first sight it could be felt weird, that the IC need high negative supply voltage instead of positive. So in my case it need 5V logic supply, -27V VFD supply and a 2.5V AC filament supply superimposed to the -27V supply.

I actually designed the whole module...

...but I had a feeling, I may did something wrong, so I broke the design into pieces, ordered the power supply boards separately, so I can test it, before send the whole module to manufacturing.

The git repo of the design is here:

 https://gitlab.com/suf/suf-electronics-vfd-futaba-15mt67gnk

To be continue..

New Arrival 9.

2023.01.05: It is kind of funny (or annoying you can judge).

My resin printer was ordered at the beginning of December in one single order.

Before Christmas arrived:

Shipment 1. - The printer itself

Shipment 2. - The wash & cure machine

Shipment 3. - 1l resin + air pure units

Yesterday arrived one single extra wash container (Shipment 4.). And still things are remaining. I don't know, how much this cost to AnyCubic.

2023.01.06: I was working a project previously. It is a replacement of the TCA530 IC what can be found in many FM radios before the era of the digital synthesis (PLL). It is a precision power supply for varicap diodes and AFC circuit. As it has an internal heated reference, but reside in a PDIP package, it intend to die after 30-40 years.

So I found a schematic for the replacement. I made some minimal adjustment on it, and shrink to fit two small PCBs, make it a pop in replacement (it is just higher than the original IC, but most of the cases it is not an issue).

This unit has some issues (questionable AFC performance, different reference voltage), so I intend to develop a v2 version, but now, from my own ideas and not a publicly available circuit diagram.

For this I was eagerly needing a working original IC.

I ordered two, it wasn't cheep. Arrived. One of my family members took the package.

It was put somewhere in the flat, so disappeared forever.

Ok, so ordered second time, now it is here

No, please don't even ask. It is not for sale. At least until, the v2 replacement is ready.

2023.01.09: The local government operated post are mostly a bunch of idiots. A package arrived for me to a post office, what is not the close one to the delivery address and not the central distribution center. They just put there (I guess) randomly.

Anyway. Picked it up:

Finally: spare screen protector, vats, fep foils arrived. With this my Anycubic order is complete. Five separate shipments of one single order. I think it is neither economical nor environment friendly. 😕

Anyway, I can start my resin experiments as soon I get there, to have time for it.

Same day. Currier came:

Big ass ESP32 board. Ordered it for some USB/Bluetooth HID experiments. I've an idea in my mind, so, we will see (as soon the current projects ready)

Same shipment:

Four different microphone module. I need it for my current project. I'll write about later. It has a same secrecy as my Melodyn project was - it can be presented when the surprise factor is over. In mid March.

2023.01.14: I was on the monthly HAM flea market as usual in the last few month.

As previously this time also picked up some interesting things.

AC milivoltmeter. Yes I know it is East-German, it is not the best quality. But it look clean, and I guess for $15 still worth it. I wanted to have an analog AC millivolt meter, but two channel dual needle configuration, but for a while, I can use this if needed.

A bonus thing (unfortunately, not mine):

It is a Bizerba weight scale large VFD display. Got it from a friend on the flea market, to do the hard work of reverse engineering, additional hardware design and driver writing for Arduino.