- 2023
- Nov
- 26
A Heathkit IM-1212 from the Fort Wayne Hamfest - making it work again.
One of the things I picked up at the Fort Wayne hamfest was a Heathkit IM-1212 NIXIE DVM. This device was sold as a kit, and was also known as the Bell & Howell IMD 202-2, as well as a DeVry branded unit. They were all the same, with different branding on the front panel.
The device itself is a 2 1/2 digit meter, and uses discrete components - all ICs are common TTL stuff - to do it’s work. It’s not the most accurate thing in the world, but I imagine it was designed to help you learn about A/D conversion and other concepts while giving you a device that you could (mostly) use at the end.
This unit was sold as working, which I verified with a 120VAC inverter/battery pack from the tool company in the harbor. I offered the guy a $20 for it, which he accepted and I took my purchase home.
It’s not in bad shape for the age, a bit of discoloration on the front panel and the obligatory tape residue on the top of the device.
It came with the original instruction manual, which is useful for troubleshooting any issues.
All of the tubes are nice and bright like it doesn’t have many hours on it. Even the NE-211 bulbs that are normally shot don’t exhibit any flickering or problems ionizing.
I did notice a few issues, there’s a rattle inside. Something is broken. The negative jack is also loose, which is probably just a nut come loose. The device also doesn’t respond to any input - something to do with the loose negative jack, perhaps?
Time to open the top cover. Notice the line of big beige resistors on the left and the one blue specimen at the bottom? These are calibration resistors, and one had apparently broken at some point, as the rattle was the remains of an old part. The original owner hadn’t removed the debris for some reason.
You’ll also notice there’s a number written on the paper cover. This is the DC calibration voltage as provided by Heath. It’s wrong, so ignore it and get a good 3 2/3 digit meter and measure the DC cal point. Mine turned out to be 1.901, so I used that later during calibration.
I discarded the broken pieces and looked at the negative jack. Sure enough, the nut was backed off, and that was because the cheap plastic threads on the jack were worn. While it tightened up, one more turn would knock it back. That will have to be replaced if I want to put this into service, but I think where it’s going it will be connected and let set as a monitor device.
The loose jack was also the cause of the no reading issue. The loose jack and solid wire insured the wire itself broke. That was an easy fix, just a quick re-solder and we’re back in business.
Time to hook it up to a power supply and see what it reads. It’s close, I guess for something of unknown quality it’s fine. As I stated earlier, these weren’t known for being the most accurate of devices, nor were they known for staying where you put them. Fortunately, the DC calibration is pretty easy, just requiring the device having been on for some time to temperature stabilize.
I’ve already posted the DC calibration procedure for someone, so if you haven’t read it you can do so here: https://wereboar.com … t-im-1212-nixie-dvm/
I don’t think there’s much more to say about this device that hasn’t been said already by many others. I’m planning on making a small board that switches between the different voltages in my network rack, so that may show up at some point. Until then, stay tuned for pictures from Fort Wayne and the Scott Antique Market at the Ohio Expo.
- 2023
- Nov
- 23
DC Calibration of the Heathkit IM-1212 NIXIE DVM
The Heathkit IM-1212 DVM is a 2 1/2 digit multimeter sold by Heathkit (obviously!) as well as under the Bell&Howell name as the IMD 202-2. They are the same unit with a different name on the front. I’ve also been told that DeVry had one marked with their name as well, but I’ve not seen one of those.
(Hi hobbyshoppin…will copy the actual relevant portions of the manual for you next week!)
These are not the most accurate meters, and are hard to keep in cal. DC calibration is fortunately, fairly easy.
We’re interested in 4 spots in this meter, indicated by the red outlines in the image. They are, from left to right:
1: The DC CAL test point.
2: The OSC adjustment.
3: The ZERO adjustment.
4: The DC CAL adjustment.
(click on the image to enlarge)
What you’ll need:
A small flatblade screwdriver to turn pots. A plastic alignment tool will work best if you have it.
A meter with at least 3 1/2 digits of accuracy
A cliplead
Start by removing the screws for the cover. Look inside and make sure nothing looks burnt or damaged. If you’re good, put the cover back on, and apply power to the unit. Turn it on, and set it to DC Volts, “2” range.
Let it set with power on. The manual suggests 15-30 minutes warmup time, but I say give it a few days. You want this thing to be as warm as it’s going to get. Just let it set. It needs to be nice and temperature stable.
When it’s warmed up, remove the top cover. Start by looking at the paper on the transformer. There’s probably a number written there. Ignore it. That’s the DC CAL voltage as suggested by Heath. It’s wrong.
With your negative lead on the black jack on the front (all measurements are in reference to this jack) measure the DC voltage on the DC CAL test point. It should be 1.9xx-ish. It may be 2.xxx or 1.8xx, but note that to 3 digits. For example, mine states 1.936V, but the actual measurement was 1.901V. Note your voltage somewhere for later use.
Note: This voltage is generated by two crappy carbon comp resistors, so it’s going to drift as well. If you have something with a known voltage around 1.9V, then use it instead!
Jumper the red and black jacks. Using the ZERO adjustment, turn it until you get to 0.01, and then turn it until it JUST goes to 0.00. Heath suggests that at this point, the reading should flicker between 0.00 and 0.01. I usually just set it to 0.00 and don’t worry about it.
This part isn’t in the manual. I don’t know if it will help, but it may get you closer to the specified oscillator value…
Change to KOHMS and open the top. Let it set for a while open circuit so you’re getting the oscillator number. When it’s stopped changing, note it. Put the cover back on and observe the drift. When it’s stopped drifting, note this value as well. When you have the top off to adjust the oscillator, adjust it so that you’re accounting for the drift - i.e. if it drifts up, set it X counts lower, etc.
Or, just do what the manual says and…
Remove the jumper and change the input to KOHMS. The OVER lamp should be lit at this point, you want an open circuit. Using the OSC adjustment, adjust so the display reads .85.
Change back to DC Volts. Connect the red jack to the DC CAL test point. Adjust the DC CAL adjustment so the meter reads as close to your measured voltage as possible. Round the number based on the last digit of your measured voltage. Round up for 6, down for 5.
At this point, you should be able to get a good DC measurement out of the device. Be aware that it’s not very accurate, and on the 20 range you’re going to have a +/- of 0.5V. You may want to go through and adjust things again later after the unit has warmed up more, but you’re never going to get a super accurate reading out of this device.
That’s it for DC. If you want to do the rest of the calibration, I’ve copied the relevant portions of the manual and placed them here:
- 2023
- Nov
- 21
Notes from the Fort Wayne Hamfest
Fort Wayne was pretty good this year, and I have a lot of pictures to process and upload.
In the meantime here’s a bit on a device I picked up. It’s a 2 1/3 digit DVM made by … I don’t know. I’ve seen it sold as Heathkit, Bell&Howell, and others. It’s not the most accurate thing in the world, but it was easy to put together and looks to be a good tool for teaching basic A/D concepts. It’s very drift-y, and from what I can tell was known to be such even when it was new. It’s still cool, however.
It required some minor work and adjustments to get it up and running, which I’ve documented and will post later - but in the meantime, here’s the device doing integrations on a low speed sine wave. It counts as fast as the TTL silicon will allow it.
(If the below gif doesn’t play, click on it.)
Stay tuned for more electronics junk good stuff!
- 2023
- Oct
- 25
Testing the Aliexpress Supercapacitor UPS.
Some time ago, I picked up two supercapacitor UPS devices from Aliexpress.
They’re 22F, 12V in, 5V out, and run about $23 per with free shipping. They’re available here: https://www.aliexpre … 256804670683100.html if you’re so inclined. This isn’t a suggestion or reccomendation, just one of the places you can get this item.
Within the sales page is an output time chart:
But who knows if this is correct, it wouldn’t be the first time that a vendor has overrated the capabilities of a new technology. I decided to set up a test of my own to see what happens. For this test, I selected the following items:
A 2A 12V switching wall wart from an old hard drive.
The Supercapacitor UPS, “Bundle 2” from Aliexpress.
A 0-10V laboratory meter.
A 0-1A laboratory meter.
A Rat Shack “Micronta” digital voltmeter.
An Orange Pi 1 with display in a “Monitor-IO” case.
Cables and connectors.
Specifications of the UPS itself:
Input: 12V via screw terminals or barrel jack.
Output: 5V at 3A max via USB-A or screw terminals
Charge and power indicator lamps
There is a version that is 12V output on both the screw terminals and USB-A jack, so if you make a purchase insure you are getting the right model!
Hookup is relatively straightforward, so I’m not going to draw a schematic, but: 12V goes in to the UPS, and comes out the 5V side. A voltmeter is across the load, and an ammeter is in series with the load. The load, of course, being the Orange Pi 1.
The Orange Pi 1 is an Allwinner H3 Quad-Core A7 CPU and has 512MB onboard. It’s booting from a uSD card and powers a simple 2-line display with RGB backlighting. It’s currently running the standard Armbian build with a ping monitor program.
Originally, this device was sold by a company called Monitor-IO as a network monitoring and intrusion device. When the company shut their doors (and the backend of the device,) they provided a simplified version of the applications for those of us who had the devices. Other than their special sauce, it’s simply a standard OP1 with Linux.
Booting the device reveals that it will spike to about 400mA of current draw, but settles down to an average of around 180mA with minor spikes as the network is accessed. These are very small in time and current consumption, so they don’t really affect much.
Voltage output while charging is 5.35 volts, and current draw on the testbed is about 180mA.
First test was to see how long the device takes to charge. With 12V 2A input and 180mA output, I observed the following approximate times. These are times indicated by when the charge indicator LEDs lit fully, and are approximate because some of it is subjective:
1st LED (Red): 180s
2nd LED (Grn): 240s
3rd LED (Grn): 330s
The LEDs have a very fast flicker while charging, and you can kind of see this when you squint at it. When the flicker vanished, I assumed that the device had reached full charge, which happened at about 5m 30s. I’m going to assume that no matter what kind of current you give it, this is going to be limited as not to short-circuit the input power supply when the capacitors are charging.
Second test was to see how long the device will hold itself up before charge is exhausted. As with the charging test, each of the times is when the appropriate LED went out. I did observe a voltage output change during this time, which is noted below. Each of the noted times is from input power removal, and again, is approximate.
Power drops to 5.00V: 5s
1st LED (Grn): 240s
2nd LED (Grn): 280s
3rd LED (Red): 346s > power off.
The output at power off drops to 0.603V, and stays there for some time.
At 180mA, you get well over 5 minutes of up-time to safely shut down your machine. If we extrapolate this up to 1A, you should get about 55s of up-time, which corresponds to the life chart and is still plenty of time to shut your machine down safely, assuming you do it within a few seconds of power failure. The device offers a soft-switch to signal power off events to the device in question, if you’re so inclined - but I did not test this as it’s not going to meet my needs. I’m planning on spinning up a simple board with some reed relays on it to provide my monitoring equipment a dry contact for notifications.
In all, this is fine device for smaller SBCs and any device that’s running on 5V, and you don’t have to worry about replacing batteries. It’s not going to be useful for some of the newer devices that require up to 5A of 5V, but for the device in question (and probably things up to the Pi2/3) it’s a good, cheap solution - something that’s quite rare in this day and age.
The only things that may trip you up are the slightly high 5V when there’s input power, and the 0.603V after power off. Most SBCs probably won’t mind either of these, but if you have a sensitive device it could cause problems.
I give these devices a thumbs up, and plan on implementing a few of them around the network.
- 2023
- Oct
- 20
I finally got around to testing the supercapacitor UPS.
It’s been sitting on my desk for a while, waiting for some time. Now that the weather has turned towards rainy fall days, some time has been found (and no, I don’t have any extra, sorry!) There was nothing really surprising found, and I’ll publish my results once I get them written up into something coherent. Stay tuned!
- 2023
- Sep
- 29
Did Espressif fix their RF spurs?
Some time ago, I wrote about my experiences with the ESP8266 line of microcontrollers. Specifically, that they had a giant RF spur at 319.98MHz. This wasn’t an unknown issue, the FCC documentation (had I read it beforehand) clearly called that out. See this post: https://wereboar.com … of-cheap-technology/ for more info on that.
Recently, I picked up this little gadget from a well-known overseas marketer. It works amazingly well, although I suspect this one of having hacked firmware… The MAC it gives to the router clearly identifies it as an Espressif device.
One of the things I immediately noticed, however, was that there isn’t a spur. I was running my devices in a similar manner, they were simply consuming data while being connected to a WiFi interface. I have to wonder if Espressif has fixed that issue, or if the firmware is doing something odd to keep that in check. More investigation is needed here, and perhaps a new look at my old designs is in order.
- 2023
- Sep
- 28
An infrared camera for about $40
Within the last 10 years, low resolution and correspondingly cheap IR sensors have come on to the market. Ranging in size from 8×8 to 32×32 pixels, these devices have shown up in many projects and purchasable items.
This type of IR sensor isn’t a camera per se, but instead is a grid of temperature sensors that a processor assembles into a visible image. You could just as easily have a grid of temperature readings instead of the visible image.
One such series of sensors is the AMG88xx series from Panasonic, and probably other vendors with less recognizable names. Costing around $20 from various sites, this 8×8 sensor is cheap enough for the hobbyist.
They’re available direct from the Chinese assemblers: https://www.aliexpre … 256804493110749.html
However, for not much more you can get one assembled into a small package with a screen: https://www.aliexpre … 255801147595884.html
(These are not suggested purchase links, but examples of item cost. I’ve used Aliexpress quite a bit over the years, you generally get what the listing shows - just be careful and make sure you’ve selected the correct item, as they tend to have multiple items in the same listing and sometimes you don’t pay attention and get the wrong item.)
I purchased one of the fully assembled units, received it the other day, and gave it a try. I received exactly what was shown in the listing, a camera module, a screen and CPU unit, all assembled into a couple of pieces of plastic sheet.
There’s no battery, so you have to plug it in to a USB or other 5V source via the Micro USB on the side. It comes up immediately with the image.
Here’s a hot cup of tea. You can clearly see the hot spot, even if it’s not well defined. The temperature reading is in °C, and there’s no way to change that. Not a big deal.
A glass of cold water from the tap.
And a cold drink that’s set out for a while.
This, like most devices of it’s kind, auto-scales the temperature colors so the hottest spot, regardless of actual temp, is red. That’s a nice feature and gives you a telltale as to what you’re looking at.
Physically, the device fits in the palm of your hand. There’s no focusing lenses or frills on this device, it’s as basic as you can get and still have an operational device that’s not just exposed circuitry.
The front with screen.
The side, showing the USB port and the open frame construction.
The back of the unit with the business end of the device.
Overall? This is a pretty amazing tool for $40. It’s not going to show you detailed images of something, but it’s just enough that you could spot a hotspot on a board or piece of equipment, helping you pinpoint things for further troubleshooting.
Beyond that? It’s just a cool toy and an amazing piece of tech.
- 2023
- Sep
- 17
A Supercapacitor UPS? Does it work?
I picked up a couple of cheap ($25ish) Supercapacitor UPS devices from AliExpress. I wasn’t sure what to expect from them, but they work surprisingly well. This is a true UPS, and stores enough power to shut your device down gracefully - not hold it up for hours.
I’m doing some testing and will post my results in a few weeks. Stay tuned!
- 2023
- Aug
- 8
Checking out a Heathkit AG-7 Signal Generator
This is a Heathkit AG-7 audio signal generator. One of Heathkit’s many pieces of test equipment, this one dates to the 1950s. It has a mix of tube names (most with RCA type labels) indicating it was probably in use for quite some time.
This was purchased at the Breezeshooter’s Hamfest in Butler, PA during their spring 2023 show. It was kind of a spur of the moment purchase. I initially passed it by, but picked it up on the way out.
I really don’t have a use for this item, but what caught my attention was the label on the side. This appears to have been in the rack at a central (phone) office in Erie PA. Was this device generating the craft access test tones? How many technicians listened to this device’s output over the years? It’s kind of cool to think about that.
The telcos were big fans of stamping stuff with ink instead of putting tags on thigs. That it has an actual General Telephone sticker is neat in itself.
Top of the device is a little dusty, so it appears that it was well cared for in it’s life and not just shoved in a barn somewhere.
Similarly, the bottom seems to be in good shape.
It almost looks like it was factory built,
But there are tell-tale signs it was probably put together by someone at the phone company. There is pencil labelling all over the chassis where someone was building it and making notes while they did. That’s always neat to find and gives you a connection to the person that built the device.
The case itself is in pretty good shape, just some surface rust where the paint was thin or damaged from use over time.
Small banana slicers are used to trim the output.
One of the terminals on the front was gone, but since those come apart easily, that’s to be expected. If I wanted to put this back into service, that would be easily fixed.
Here’s something that leads me to believe this was probably being used for test tone generation. Here’s the amplitude control. Note the two holes on either side of the pointer - this looks like it was strapped down at some point to give a known output level. The amplitude couldn’t be changed if the control couldn’t be adjusted.
The visual inspection of the device didn’t reveal anything that I felt was concerning enough, and some quick checks of capacitors and other potential failure points seemed to indicate there wasn’t any immediate issues. Time to plug it in!
All of the tubes lit up, so on to checking the output. I let it warm up for a bit.
I randomly picked 300Hz as my test point, and set the dial as close as possible. The scope revealed that the device was both off in frequency vs. the dial, and had some problems with waveshape. While I didn’t do any troubleshooting at this point, I suspect that there are some leaky parts simply due to the age of the device.
I ran up the scale with the frequency multiplier control, and it seemed to be pretty stable, generating the multiple of the selected frequency. I chose 3KHz as my next test point and adjusted the output to as close as possible to 3K.
The dial was off a ways. I’m guessing the trimmer capacitors will take care of this, I just need to sit down and read the manual.
Without changing anything, I selected the squarewave output. It looks good, but drops off considerably vs. the sinewave output.
I’m not sure if this is the intended behavior, so I will again refer to the manual that I have not yet read.
Overall, this is kind of a neat piece of equipment. While it’s functionality could be exceeded with a piece of more modern equipment, sometimes it’s nice to have something that won’t be damaged (much) by accidentally having B+ on an input. If time allows, I may try and get this device up and running. It will probably require some new parts, as all of the old ones have drifted with age.
That will be a project for another day.
I’ve started working with this device: https://wereboar.com … part-1-observations/
- 2023
- Jul
- 10
Random board shot: The Atari 2600
This is an Atari 2600 “Video Computer System,” or VCS:
But you knew that already. This is the model known as the “Heavy Six.” It was made in Sunnyvale, California.
It’s a first generation model. It’s called a Heavy Six because of the six switches on the front panel, and it weighed more than later models due to the thick cabinet:
And because of the cast aluminum RF shield present around the actual processor and other circuitry. This was not present in later models:
The cabinet is held together with 8 screws, and splits easily into two halves.
Code named “Stella” when it was being developed, one of the removed features was built-in speakers. You can still see the holes in the top chassis where they were supposed to be mounted.
But that’s not what interests me the most. If you examine the board, you’ll notice that now familiar Textolite “T” imprinted in the circuit board itself, indicating the raw board came from the GE plant in Coshocton, OH.
It still amazes me how far-reaching this little town’s products were.