Category Archives: Electronics

Electronics

Micro Networks Corporation MN3010 DAC: long term stability test of a rather unconventional DAC

2015/12/04 Simon Leave a comment

Recently, I found a MN3010 chip, in a pretty fancy and unconventional ceramic/gold/metal package. Turns out, it is a DAC; but not a normal DAC – rather a 2 digit BCD DAC.

MN3010 Datasheet

Quickly hooked it up to an 8 bit port, counting in cycles, from 0 to 255… This is the resulting output:

Bottom line is about -13 volt, top is 0 V. 2 V per vertical division.its

Notice the strange steps – this is a clear indication of the “BCD” nature of this chip – 4 upper bits encoding the output in 1 volt steps, and the lower 4 bits encoding the 0.1 V digit.

Now, to put it to a test – re-programmed the counter to actually count in BCD digits, from 0 V, to -10.9 V – which is a bit above the specification – the device is supposed to output 0 to -10 V.

Next, let this thing run for about 18 hours recording the voltage at each of the allowed input codes, using a HP 34401A 6.5 digit volt meter, using a little program and GPIB cable.

These are the output voltages, as a function of time, for certain fixed codes:

… I would say, the DAC is rather stable: it consumes about 0.5 Watts, and is running warm, but it appears to be reasonably insensitive to temperature, far better than 0.1 LSB (more like 0.01 LSB!)

After recording all the numbers, some number crunching using well-known Excel…. multi parameter linear regression.

Regression analysis yields the voltage values associated with the bits, they are close, but the 0.2 and 0.4 V have some deviation. It’s a pitty I didn’t test this device about 30 years ago, then we would know if this deviation is due to age, or just the result of normal manufacturing tolerances (certainly all within specified limits).

Here, as a last graph- the total deviation (which contains all error sources, including any offset errors), accordingly, the output tends to be 0.005 to 0.02 V (0.05 to 0.2 LSB) low, digital code vs. actual output voltage. Pretty good (limit is +-0.25 LSB), still.

Now, let’s keep this device another 30 years, and repeat the test…… I will keep you posted.

Attenuator calibrator (objective: a really precise and accurate apparatus)

Micro-Tel Precision Attenuation Measurement Receiver: an all-electronic manual for an almost all solid state device

2015/12/02 Simon Leave a comment

Look at what I have here, finally, an (well, almost, 1 page missing) PDF manual for a Micro-Tel 1295 Precision Attenuation Measurement Receiver. Including all schematics…

…a pleasure for the eye and joy forever!

If you have any rare manuals, let me know, much appreciated!

Various

Ultrasonic Pest Chaser: scare way all the rats, squirrels and other furry creatures….

2015/11/30 Simon Leave a comment

Winter approaching, all the pests of the world would like to hibernate in my attic. And around the house, an increasing number of squirrels is feeding off the birds’ food. But hold, for every problem, there is an electronic apparatus that can solve it, it this case: an ultrasonic pest chaser.

First of all, we need a random ultrasound signal generator. Tests have shown that frequencies in the 18 to 30 kHz range are best, and that not all animals respond to the same frequencies. So we need a cover-all solution. Furthermore, animals will get used to certain noises, even 105 dB ultrasonic noise. So we need to build-in some surprises. Sometimes, the machine will be quiet, then it will come up with all kinds of nasty sounds. Sure enough, at high level.
This is achieved by a little microprocessor, an AVR ATmega8, but you can use any micro of your choice. Please check out the source code – the sounds are generated by using certain pre-set sequences of breaks, durations and sound frequencies, and these are rotated in a repeated (but very long) pattern. The pattern won’t repeat to soon, because prime numbers have been chosen for the lengths of the sequences, thus, they appear almost random for the listener (only those with ears able to receive high frequency noises like this).
There is also a LED indicator signaling the ON state of the ultrasound. Even if you can’t hear it, please stay away from the speakers – these >100 dB may damage your hearing without any prior notice. Keep children away. As always, this post is for your education only, don’t try it at your home!!

The signal generator schematic is as simple as it gets – frequency is derived from a 4 MHz crystal, via TIMER1 of an ATmega8. Some auxiliary circuitry is used to derive a 5 VDC rail from the supply voltage (anywhere from 10 to 30 V, depending on the speaker).

The power driver uses two NPN transistor and a MOSFET to provide sufficient current for the speaker. The speaker, some are under test, more about them later. Piezo high frequency speakers are the speaker of choice for this application.

Some pictures of the boards – all build on plated-through FR4 perf board, this will last a long time even when use outside.

A test, using a 10 Ohm load resistor, and a 40 kHz drive signal. The MOSFET is switching nice and fast, no issues. For the speaker, it might help to couple the (capacitive) piezo with a suitable inductance, and to add a DC decoupling capacitor (about 1 µF, pulse resistant type). You can see that the resistance of the MOSFET in ON state is about 1 Ohm, current is about 1 Amp, for a 12 VDC supply voltage – and 0 V is one graticule up from the bottom of the scope.

Finally, a test of the circuit, frequency (Hz) vs. time (seconds). This nicely shows the “random” nature of the noise, with breaks of various lengths in between noise bursts. Poor squirrel, poor rat – but they have a choice: keep out of harm’s way, and out of the attic!

This is the microprocessor code, avrgcc.

marder1_151130

Various

Compact Fluorescent Lamp (CFL) TP120-13MSL, 13 Watt: some circuit analysis

2015/11/27 Simon 1 Comment

Quite honestly, I don’t like these compact fluorescent lamps (CFLs) too much. They save energy, maybe, but the light produced is not really appealing, and in the long winters here, some extra heat produced by an ordinary light bulb is much appreciated anyway.

Having a few defective CFLs around, I could not resist to open one up and check inside. That’s the schematic.

More can be found at other sites, this is quite comprehensive: CFL Schematics (LabKit).

The circuit uses a rather small ring core transformer, two primaries, for feedback, 3 turns each, and a secondary, 9 turns. Two transistors MJE 13003 (in TO-92 package) are arranged to form an oscillator circuit. These transistors can handle 600-700 V no problem. The DIAC (BA3) forms the starter circuit, giving a first few pulses to the oscillator, when the lamp is still high-impendance (prior to ignition). Once the lamp has started, the D5 diode will disengage the start-up circuit.

The transformer:

Below, wrapped in blue tape, and with an E-E ferrite core, that’s the choke, about 1.6 mH inductance, which is part of the lamp’s resonant tank (along with C3, C5, and the secondary transformer – and C7, which will play a minor role, because of its comparatively large value).

Various

HP 8481A Power Sensor: why are they all blown?

2015/11/05 Simon 13 Comments

A remarkable HP product, the HP8481A sensor. It appeared on the market about 1974, and still today, these devices are very much thought after. It works from about 10 MHz to 18 GHz, -30 to +20 dBm.

Quite some detail about this sensor can be found in the HP Journal, 1974-09 edition (pages 19ff).
There is says that the sensor can withstand 300 mW power, and even 0.5 Watts for seveal days. Still, there are many sensors around that are blown – why do so many people connect them to 0.5+ W transmitters and destroy them along the way? I have no idea!

Here, a quick glance at the internals:

Note the capacity values – measures: 3.5 nF at the input, 3.0 nF at the output. This is all real gold on sapphire substrate!

Noise Meters and Noise Figures

HP 8970A Noise Figure Meter: A7 voltmeter assy fix

2015/09/29 Simon 2 Comments

Finally, some capacitors arrived, Panasonic ECW FD type, polypropylene dielectric. These are very much suitable for any type of active filter or sample/hold circuits, thanks to their good capacitance stability, and low dielectric absorption.

Dielectric adsorption, not something specified on the datasheet. So I did a quick test, using a 50 Volt power supply, a 100 Ohms resistor, and a high-impendance (10 GOhm or more) voltmeter. Test follows this sequence:
(1) Charge capacitor for about 10 minutes; make sure to limit charge current to a few 10s of mA.
(2) Discharge for 10 seconds, using a 100 Ohm resistor.
(3) Measure voltage and record maximum value (V_measured) – typically, this takes several seconds.
(4) Calculate: V_measured/50 Volt *100%, the number obtained is a measure of dielectric absorption, in %.

Results: 0.005% for the ECW FD (Panasonic brand, PP dielectric), and 0.09% for the original cap, HEW-446 series (TRW brand, PET dielectric). Not bad, rule of thumb says that PP has 5x lower absorption than PET, well, but don’t quote me on the numbers measured – these are just rough estimates, fair enough. Needless to say, the new capacitors will outperform the original ones by far – and hopefully last as long, or longer, 30+ years….

Another detail. Note the line on the top side of the A7 board, close to one terminal of the capacitor? This is the outer winding of the capacitive layer. This goes to ground. The ECW FD aren’t marked for their winding direction (these are non-polar caps, but still, there is an outer layer of foil, and an inner layer, and the outer layer does pick up more noise, and thus needs to go to the lower impedance connection). But the winding direction can easily be determined, just connect the capacitor to an oscilloscope probe, and hold the part between your fingers – then, swap the probe (switch ground and hot connection). You will see different levels of noise on the screen, mainly, 50/60 Hz hum. Select the connections for lowest noise, and the ground lead of the oscilloscope probe will then indicate the outer layer of the winding. Best, mark it with a felt pen.

R820T/RTL2832U USB SDR: Various hacks and measurements

USB RTL SDR 28.8 MHz Reference: dividers, PLL, success

2015/09/13 Simon Leave a comment

With the 28.8 MHz VCO design established, all we need to move this project on are divers for the 28.8 MHz (VCO) and 10 MHz (Reference) signals, a slow-acting PLL, and some auxilliary circuitry to feed the 28.8 MHz back to the RTL SDR.

The 28.8 MHz and 10 MHz signals are AC coupled with about 1 kHz input impedance, this is quite common for any 10 MHz reference signal input (used for various kinds of test equipment). These signals are then amplified/limited by unbuffered inverters, 74HCU04. This is a very cost-effective and easy solution, the HCU04 has push-pull outputs, and input clamping diodes. Still, some clamp diodes have been added for the 10 MHz input, just in case.

Looking at 28800 kHz, and 10000 kHz, 400 kHz is the largest common denominator. Accordingly, we need :72, and :25 division factors.

Division of the 10 MHz down to 400 kHz is accomplished by two 74LS90, but you can use other TTL decade dividers, these were just the circuits I had in stock.
28.8 to 400, a bit more tricky, first, divided by 8, using a 74LS293, and another LS293 that has two diodes, acting as an “OR”, to reset the counter when count 9 is reached.

Both 400 kHz signals are then compared use a flip-flop phase comparator, conveniently packaged in a 4046 PLL. For convenience, and to avoid digital noise on the 12 V rail powering the VCO, the 4046 is powered only from 5 V. This somehow limits the tuning output range, from close to 0 V, to about 3.1 V.

The loop filter is very slow acting, tens of seconds, because the objective of this PLL is to correct long-term drift of the 28.8 MHz reference, introduced by temperature, Xtal drift, etc., but otherwise not to impact its noise and oscillation characteristics.

The VCO (see earlier post, VCO design) uses a fixed capacitor to set the tuning offset, this was changed to 4.4 pF, and finally to 2.2 pF, to properly center the tuning voltage (V_tune, output of the PLL loop filter buffer) within the 4046 output range, at roughly 1.7 V.
Extentensive testing was carried out the ensure that the VCO starts up properly, even if extreme V_tune voltages are applied; as the 28.8 MHz Xtals used in the USB RTL SDR devices may vary, you will need to check the required tuning range and pullability of the Xtal. Some Xtals oscillators will stop oscillating, if you pull to frequency up or down too much, which might happen during PLL start-up. This can lead to an undesirable lock-up condition.

Here are the tuning characteristics, for 2p2, and 4p4 pF VCO capacitor values.

This is the divider and PLL board. Sure it would be much nicer to have everything completely separated, in shielded cans, etc., but I did not go to such effort. Later testing will reveal if it has any bad consequences for the 28.8 MHz phase noise, but so far, I don’t see much noise – will do a more in-depth comparison later.

Noise Meters and Noise Figures

HP 8970A Noise Figure Meter: defective A7 voltmeter assembly – temporary fix

2015/08/31 Simon Leave a comment

A broken noise figure meter, not really a good situation with so many tasks related to noise figures at hand, not only the noise source projects. So, another look at the A7 assembly. With the suspect TL072 opamp replaced by a less suitable, but known-working subsititute, the fault still comes and goes – well, maybe, in the end, the TL072 is not even at fault? There aren’t so many components around, so I checked for all the likely and unlikely things, and found – a defective integrating capacitor!

See the schematic – there are two of the same kind – C4 is the bad one (integrator cap; upper orange frame), C3 (auto-zero; lower orange frame) is fine.

0.15 µF, 100 V, Mylar, 1982 vintage, and after all these years, somehow, it has developed an intermittent fault (the first Mylar cap with such fault I have ever seen).

With no spare at hand in my tiny New Jersey workshop, I decided to swap the caps, using C3 as C4, and temporary mounted a 0.1 µF film capacitor (Wima FKM) as C3. For the auto-zero function, the exact value and leakage of the capacitor won’t matter so much, anyway.

See, how nicely it works: red – integrator charged from input voltage; blue – integrator discharged by reference voltage; grey – auto-zero; this sequence repeats over and and over again, and the duration of the reference segment is determined, after applying the input voltage for a fixed time (all controlled by LS TTL logic on another board).

0.25 V input, 1.2 V reference.

1.0 V input, 1.2 V reference.

Some quick thoughts about the capacitor; typically, Mylar/PET/polyester caps aren’t the best for integrators, because of higher leakage current, and dielectric absorption, compared to, say, polypropylene caps. Maybe, at the time, HP engineers determined that the TL072 leakage current, and other leakage currents on the board would be much larger than any capacitor leakage current; or, they didn’t want to introduce specialized parts – these axial Mylar capacitors of TRW brand were quite common in 1970- early 1990 era HP gear. These are actually not metallized Mylar/PET, but film-foil capacitors (using discrete plastic and metal foil, similar to Wima FKS-3).

Look inside the dead cap – there actually are the plastic and metal foils.

For the next few weeks, this configuration will be sufficient; then I will check capacitor stock back at the main workshop; most likely there are some Wima/Epcos/TDK FPK or MKP (PP dielectric foil-foil or metallized PP foil) capacitors around; if not, then I will just fit a pair of good Mylar caps.

Noise Meters and Noise Figures

HP 8970A Noise Figure Meter: voltmeter assy (A7) defect

2015/08/30 Simon Leave a comment

Not so good news today, after characterizing all kinds of noise sources, the 8970A stopped working. Can’t get it to calibrate properly, or to show any reasonable noise power values. A quick check revealed that the detector output (voltage proportional to the noise power measured) is good. But no proper display when activating the 8970A-internal volt meter (special functions 80, 81).

Checking various traces and signals – the issue seems to reside with the A7 assembly, voltmeter.

Red – input voltage section; green – reference voltage section (about 1.2 V); blue – auto-zero section.

How it works, quite well-established dual-slope integration with autozero – a capacitor, initially at zero volts, is charged first from the input voltage, then from a (negative) reference voltage, until zero is reached again. The time it takes to do this directly relates to the input voltage.

See here, working example (sorry a bit dim- see the triangular shape in the lower left hand corner of the scope screen).

Here, non-working condition – integrator not working.

After checking various FETs, and timing signals – the TL072 integrator opamp appears to be the faulty device. It is a strange, intermittent fault – not triggered by vibration, but appears to be intermittent with no direct external cause – maybe a defective output stage of the opamp? Removed it from the circuit; unfortunately, all spare back at the main workshop in Germany, but fair enough will get some TL072s in soon.

…. once repair is done, noise source project will continue asap!

Noise Meters and Noise Figures

TWS-N15 Noise Source: checking out some design alternatives

2015/08/30 Simon 11 Comments

So far, we have mainly been discussing series type noise sources, i.e., noise sources where neither anode nor cathode are connected to ground. Another common design is shown here – the shunt configuration (one port of the noise generation element grounded).

The assembly, more or less just a little blob of solder with a few tiny parts inside… mostly, 0603 SMD format. The output attenuator (not shown) is a 14.5 dB(!), 18 GHz coaxial attenuator.

Some quick measurements, at bias currents of 2.5, 5 and 7 mA…. still, there seems to be a lot of 1/f noise (increase of noise power at lower frequencies). This is model #1, with a 22 nF capacitor (see schematic)

Don’t really see any advantage over the series variant of the noise source. But will test further.

…Progress on another front, ordered a set of PCBs – they can be used for various noise source configurations. Not yet a “prototype”, but need to see what kind of GHz performance is available from such design, and how reproducible it is. No current source yet on this PCB – will add later, or on a separate board – to limit shielding to the RF section.

SimonsDialogs

Category Archives: Electronics

Micro Networks Corporation MN3010 DAC: long term stability test of a rather unconventional DAC

Micro-Tel Precision Attenuation Measurement Receiver: an all-electronic manual for an almost all solid state device

Ultrasonic Pest Chaser: scare way all the rats, squirrels and other furry creatures….

Compact Fluorescent Lamp (CFL) TP120-13MSL, 13 Watt: some circuit analysis

HP 8481A Power Sensor: why are they all blown?

HP 8970A Noise Figure Meter: A7 voltmeter assy fix

USB RTL SDR 28.8 MHz Reference: dividers, PLL, success

HP 8970A Noise Figure Meter: defective A7 voltmeter assembly – temporary fix

HP 8970A Noise Figure Meter: voltmeter assy (A7) defect

TWS-N15 Noise Source: checking out some design alternatives

SimonsDialogs – A wild collection of random thoughts, observations and learnings. Presented by Simon.