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Micro-Tel MSR-902C

2016/05/10 Simon Leave a comment

Today, a few spare MJ12002 transistors arrived. No time to lose, and put them into the power supply. Note that the new transistors are 1983 data code, whereas the Micro-Tel originals were 1988… fixing the power supply with old parts, but no reason to assume that these transistors have any issues with age. With such power supplies, I would always suggest to use a pair of transistors of the same manufacturer, rather than mixing up two very different devices. This is why both transistors were replaced, not just the defective part.

msr-902c 8322 mj12002

After this replacement, connected a 10 Ohms 25 Watts load resistor, and grounded the Interlock and ON/OFF lines. When powering up, the green AC ON light comes on, but not for too long. Look at the set of fuses sacrificed in the process:

msr-902c pwr supply rep fuses

Another set of tests – no issues found, all working fine. Something must be loading the power supply, and I can’t get any negative voltages out of it – but there must be at least one negative rail to provide -15 V to the various opamps in the receiver.

Not to long and the culprit was found – a shorted tantalum, a T310 series Kemet tantalum, directly at the – what turned out to be, -18 V output. Check out the date code. Why did Micro-Tel put a 1979, week 38 dated device, in such kind of expensive and specialized equipment (other parts suggest that this unit was made about 1989, at a price of about -50k – that’s about k in today’s dollars…).

msr-902c tantalum

Some tests show that there is a +18 V, -18 V, and a +12 V output. All are routed through feed-through capacitors. A fair bit of effort, and cost!

msr-902c pwr supply output

First test with the actual receiver connected –

msr-902c first pwr test

– connected the 1-18 GHz tuner – a bit of a cable mess.

msr-902c test setup

To test the basic functions, like, IF chain, detectors, etc, a 1.5 GHz test signal from a HP 8642B was routed to the tuner. And, to my greatest satisfaction, the MSR-902C is actually receiving!

msr-902c receiving 1.5ghz

1 kHz AM modulation…

msr-902 receiving am

… also tested the FM and AM detectors, both in sweep and fixed modes, the AFC, the IF gain, the marker – all working. Also the 8-12 GHz, and 12-18 GHz ranges, working fine. Clear signal down to -105 dBm input. So all working and pretty well tune.

msr-902c 8 to12 range

Unfortunatly, this is not the case for the 2 to 8 GHz ranges – the frequency display is not showing a reasonable value – not sure what is going on here. Maybe something with the band logic, or the signal multiplexers (see the MSR-904A repair story – these instruments are notorious for defective CMOS multiplexers).

msr-902c 2 to 8 ghz ranges defect

So far, so good – at least in some bands, we would receive satellites, or signals from other galaxies, given, there aren’t many strong sources out there, in space, and all the other solar systems, too far away!

mj12002tantalum short

HPAK (HP Agilent Keysight) 3562A

2016/05/09 Simon Leave a comment

Here, Thanks to Michael from Zurich, Switzerland, and for the benefit of everyone with a 3562A showing similar signs of disrepair:

The 3562 A shows a fault code, is on the A2 (SYSTEM CPU/HPIB) error code 19, which means Monitor RAM Test Multiple Monitor RAM failures.
All voltages checked, and they are OK, the ripple is OK and the clocks are OK too. Everything was OK, no smoke, but I still had to solve two issues.

Issue (1)
Non-working Display Unit HP 1345A

First of all I guessed that this issue was coming from non-working A2 (CPU) but installing the test jumper to get the test screen did not work. Measured the voltages on top of the HP 1345A. These did not show any issues (no shortened tantalum capacitor) on +5V/+15V/-15V. Checked a few more voltages but not the +105V.
So I removed the HP 1345A unit to do a visual inspection and noticed the defect on the A3 board (Low Voltage Power Supply). Q1/Q2 did not look so good.

HP3562-1

For sure without +105V we do not get any picture from the HP 1345A. I removed the faulty Q1/Q2 and solder some test cables for +5V/+15V/-15V/+105V to A3 to power the assembly from an external power supply. Lucky me, no other defect and the test picture came up.

HP3562-2

I decide to order SG3524 (pulse-width-modulator), MJE180, and all capacitors of the A3 to replace them all. After the rework on A3 I carefully powered up the +15V supply which is used for the DC/DC converter to generate the +105V and measured the current.

See the re-worked A3 assy:

HP3562-3

No issue seen anymore, the +105V is working. I added a 2.7k resistor to create a nominal load (approx. 37mA) on the +105V path to adjust the +105V. Just to know what was causing the burned Q1/Q2 I swapped the new SG3524 with the original one and I see that the current was increasing like hell when slowly increase the +15V voltage. So I guess the major problem was a defect SG3524 here.

Issue (2)
Faulty A2 board with hex error code 19

After installing the now working HP 1345A back into the HP 3562A I got a bit more detailed information about the A2 problem.

HP3562-4a

It says that there is a problem on the low byte SRAM on A2. To ensure that nothing else causing this problem (bus issues) I removed the A2 from the cabinet and it can be operated completely standalone. From the LED on A2 I still got the same error code as before (when A2 was installed) so at least there is no other
board causing this issue and I really can focus on the A2 board. First I checked all signals on the two 32kx8 SRAMS (U212/U211) with a scope but I did not see anything defect, everything looked so far good (no shorts, activity on all signals, etc).
So I attached my nice Philips logic analyzer.

HP3562-5

Playing a bit with the logic analyzer, but did not get any more results so I believed what the monitor test logs said and replaced the low byte SRAM (U211) with a new one (ordered 70ns ones from Mouser).

HP3562-6

After replace the SRAM the self test is passing on the A2 and it’s now time to install the A2 board back again in the
HP 3562A cabinet (and crossing fingers!!!!!).

With the changed SRAM, my HP3562A boots up without any other errors and issues and is ready to be used again!

HP3562-7

1345a repairsram repair

Micro-Tel MSR-902C

2016/05/08 Simon Leave a comment

With no manuals available, some investigations were carried out to better understand the workings of the MSR-902C microwave tuner, which has a 1 to 18 GHz range, good noise figure, fully-fundamental mixing with 3-stage preselection over the full band. IF output is 250 MHz, so the tuner can be combined with any resonable SDR or other modern receiver, as a down-converter, offering about 4060 MHz bandwidth, and 60 to 70 dB image rejection, and huge capacity to deal with out-of-band overload signals.

This is the rough scheme, leaving out all ordinary electronics in the case, just the microwave parts (note that there is another SMA attenuator in the feed line of the splitter, coming from the 8-18 GHz YTO, not shown in the sketch).

tuner1to18 scheme

Essentially, there are two inputs. One covering 1 to 12 GHz, and another one, covering 12 to 18 GHz. The 8 to 18 GHz YTO is used for both bands, and PIN switches are used throughout to route the signals.
The IF goes through a 300 MHz low-pass and a +13 dB monolithic amplifier.

Note that there are some different/earlier versions of the MSR-902 and maybe also MSR-902C which use a slightly different configuration, with a LO doubler. Maybe the could not get proper 8-18 GHz YTOs at the time, at any resonable cost, and had to resort to another topology (using a doubler) for this reason. However, I have never seen any of the earlier tuners, and can only report what I heared about them, with documentation on these units being almost completely absent.

tuner1to18 case

tuner1to18 view1

tuner1to18 view2

tuner1to18 view3

tuner1to18 view4

tuner1to18 view5

For some of the key devices, see references below. Glad not to show list prices, as these would quickly add up to USD 10 or 20k, for all these microwave parts. Not to mention that these are all US made, most advanced and highest grade components of their kind. Datecodes are from the late 80s, mostly 1988, but still today, there aren’t much other options around to build a tuner of this kind. Maybe there just aren’t enough entities around that can afford such device nowadays, and software and digital signal processing certainly have contributed that todays devices can achieve perfect results even with less expensive, heavy, and energy-consuming parts. Still it is very instructive to study the design of this tuner. It even has a LO sample output, and with some effort, all the YTOs could be phase locked with relative ease (using GeSi dividers, etc).

anaren 70119

qbh-101

narda 4016d-10

narda 4202b-10

anaren 42040

pin switch american microwave corp SW-2181-3

american microwave corp sw-218-2

avantek av-7104

norsal dbmb-2-18

18 ghz tunerMicro-Telmsr-902c

Time Interval Counter

2016/05/08 Simon Leave a comment

A quick update on the clock monitor/time interval counter project, TIC4 Time Interval Counter. Main objective is to have a clock analyzer that will keep track of every tick of mechnical clocks and watches, in particular, of one of my precision pendulum clocks operated in Germany. These clocks are pretty accuarate, but are impacted by air pressure and temperature fluctuations. Ideally, rather than the air pressure, it would be great to measure the air density directly, but there aren’t any easy ways to do this (might be considered for a project later).

The TIC4, we have already discussed, it is based on an AVR Atmega32L, which eventually will be running of a 10 MHz OCXO ultra-stable clock, provided by a Trimble OCXO, more on this to come. For now, the circuits are running on ordinary crystal oscillators, fair enough.

The TIC4 circuit has now been combined with another Atmega32L, which I call the “controller”, aka “Logger5” here. Its only function is to wait for a TIC event to happen (timestamp received), and the the determine (room/clock) temperature, air pressure, and real time (from a real time clock, which is not very accurate, just for the purpose of keeping track of actual time and date, UTC time plus minus a few seconds, e.g, to correlate clock issues with events like earthquakes or sun storms…).

This setup represents the temporary “TIC4LOG5” wire rats nest, which will be put into a proper case once all has been tested thoroughly.
tic4log5 scheme

For the TIC4 and Logger5 Atmegas to work together, they need to run on the same serial baud rate. With the desire to run the logger at 16 MHz, and the TIC4 at 10 MHz, this leaves 38400 baud as a good compromise.

baud rates

Some small console programs are used at the host PC to gather the data, and store them in files, about 4 Mbyte a day, for 1 s pendulum, or 40 for the 10 Hz clock under test now.
All has been designed for clocks up to about 10 Hz, but the circuit can work up to 100 Hz no problem, provided that the pressure measurement (which takes about 10-25 ms, depending on the resolution mode – selected the ultra high mode, 25 ms per sample).
A note on the BMP085 – this is a quite common part, and pretty ordinary to program and work with – typical accuracy is +-1 mbar, with max. 2.5 mbar specified. Typical noise is about 0.05 mbar, but can be significantly reduced with averaging (there aren’t any fast second-time-scale pressure changes anyway).

That’s how the console works away: recording RTC (in unix time seconds, counting the events, recording the timestamp, temperature and pressure). Two files are generated, one the has the full data, and a second one that only records to event numer (TIC events recorded- and reconstructed to actual clock ticks in case a few ticks are missed) and the absolute clock deviation (time gained or lost, in seconds). For those more familiar with electronics engineering, this time gained or lost is nothing else than the phase shift of the clock under test vs. the 10 MHz precision ultra-stable OCXO, measured in seconds.

For test purposes, and to get a lot of TIC events, a 10 Hz clock source is in use as the test clock. This will be replaced by a pendulum clock, or mechanical watch, eventually.

tic4log5 clock
The boards and cables…

tic4log5 assys

…and their output, one data package, 29 bytes, every 100 ms.

logger

Some records of the last few days (pressure is as-measured, no corrections, location is Westfield, NJ, USA) – all working pretty well with no hick-ups or restarts so far!

day513

day514

day515

day516

day517

Also the Allan Deviation looks ok, and plenty accurate to measure the drift of even the most precise pendulum clocks, or similar. From the temperature effect, it seems that the test clock is speeding up a bit, with increasing temperature, but overall the effects seems to be just some random drift. Hope you also notice that the workshop here is nicely thermostated at about 22.3+-1 degrees centigrade.

allen dev 1

With the software now pretty much established, it is time to look at the precision clock source. Sure, it would be best to run this of a hydrogen maser or caesium clock, but all a bit too much for the given purpose, und consuming too much electricity. So I settled for a Trimble 65256 OCXO (oven controlled xtal oscillator), having a few of these on hand. They run at 12 V (note: which needs to be well stabilized, otherwise you will get a good amount of phase noise – not relevant for this application, but for others), consuming about 0.3 Amps, chiefly, 4 Watts.

tic4log5 trimble 65256

The output of the Trimble is a sinewave, about 3.6 V p-p when terminated with a few kOhms (no need to terminate such osciallators in 50 Ohms). This signal can’t drive the Atmega32L directly, it needs to be properly squared up. This is acomplished by a 74HCU4, which also generates an auxilliary output 10 MHz signal, handy for other uses, and for alignment of the Trimble vs. a GPS or DCF77 frequency standard.
The OCXO may drift about 10e-8 per 10 years, 10e-1010e-9 per day. This is 10 to 100 microseconds drift per day. Not sure about the Trimble units, but they seem pretty good based on past observations.

tic4log5 trimble squared

Everythings squared up properly, x axis is 10 ns per div. Well, this is close to to the limits of the 60 MHz BW scope used here.

tic4log5 trimble risetime 10 ns per xdiv

Some data on the Trimble 65256 units – interestingly, they have a 2.6 V reference, but the VFC (variable frequency control) needs to be set to about 3.2 for this unit, to get exactly 10 MHz.

tic4log5 trimble 65256 serial 12315-10040 connectors and data

Here are some of the key source files, for those interested:

tic4 avrgcc tic4_10mhz_stable160423

logger5 avrgcc logger5_stable160430

console data logger log5_main_stable160501

USB control program log5usb_main_stable160430

tic5eval R script to make the daily plots

bmp085data loggerds1302ticTime Interval Counter

Micro-Tel MSR-902C

2016/05/06 Simon Leave a comment

A few days a ago, a most intriguing briefcase arrived, brown color, looking like the late 70s… Samsonite. It is heavy! Really heavy!!

msr-902c briefcase

Inside – a fully equipped MSR-902C receiver, including all cables (which are rare, and extemely expensive to fabricate, because they use special military connectors). This receiver can more or less receive any signal, down to very low levels, and comes in 3 modules, the actual receiver, a 1-18 GHz tuner, and a 18-26 GHz tuner. Other tuners and harmonic mixers were also available from Micro-Tel, but most likely, not many of these have ever been sold.

msr-902c view1

A brief description of the MSR-902, which is very close to the 902C:

msr-902 description

Unfortunately, there is very little literature or even manuals on the MSR-902C, no instructions, no schematic – fortunately, is shares some circuits with the MSR-904A, and 1295 Micro-Tel receiver, and it is an all-discrete construction, with a lot of wires and circuit boards, so it is repairable, even without schematic (just taking 10x longer….). Should you have a manual, or any other related documentation for the MSR-902C,

Inside of the main receiver (the tuners have not yet been touched), a most amazing combination of wires, switches, boards, and so on. All hand-soldered in Maryland, USA.

msr-902c wires

msr-902c wires2

msr-902c wires3

It is a marvel of engineering, but, currently, not in working order. It blows the fuse, as soon as it is connected to mains power. Something wrong with the power supply. After removing a cup full of screws, here it is.

msr-902c pwr supply

Strongly shielded by a thin magnetic shield, all nicely machined and assembled. Now all has to come apart for repair.

msr-902c mag shield

The internals of the power supply, a good number of boards and parts. The power supply can either work from AC mains, or from 12 VDC. The 12 VDC section appears to be find.

msr-902c side view

msr-902c top view

After some tests, found the first suspect item, a full short on one of the MJ12002 transistor that drive the primary of the switchmode power supply converter.

msr-902c dead mj12002

msr-902c transistor short

It a quite old-fashined part, but could still find 3 pieces, USD 5 each. Not cheap, but OK.

msr-902c pwr transistor mj12002

Once the transistor had been removed, time for some checks of the drive circuit. This circuit is based on an MC3420 switchmode controller.

msr-902c pwr supply disassembled

As you can see, the switch mode regulator is working, just no drive transistors around that could actually drive the transformer. But will be only a matter of days.

msr-902c pwr supply drive signal

For those interested, here are the specifications (of the very closely related MSR-902).

msr-902 specifications

More to come – stay tuned!

Micro-Telmicrowave surveillance receivermj12002msr-902cpower supply repair

Miscellaneous

2016/05/02 Simon Leave a comment

The world could be a better place if all people would agree to use the same measure, voltage, frequency, etc., but this is not going to happen soon. For me, constantly moving forth and back and living on various continents, this causes additional hardship. In the US, I own a 1″x30″ belt sander, which is available from Harbor Freight, at about USD 50. That’s a remarkable price, because the unit is actually quite well-build, has roller bearings, polyamide rollers, a motor, a cast-aluminum case, a base plate, and so on. No idea how the Chinese make this for less than USD 50 – the 4 6202RS bearings alone are more than , if not more.

beltsander hf

Moving back to Germany soon, this nice litte machine will be a heavy doorstop – because there ain’t no 115 V power in Germany. What about the motor?

belt sander motor

As it turns out, it is a capacitor motor, more precisely, a permanent split capacitor motor – the capacitor remains permanently connected to one of these windings. Such motors don’t have massive torque at start-up, and are typically used for fans, pumps, and the like. While some of these motors can be easily re-wired to 230 V, the belt sander motor only has 4 wires coming out.

So, we need to have a look inside. Make sure not to damage any of the windings!

beltsander 115v wiring

A quick schematic – there are two main coils, and one started coil. Great! This means, we can rewire it…

beltsander schematic

Be sure you know what you are doing – this is all mains voltage, and the wires need to be properly wrapped and insulated (especially, the now exposed connection point inside of the motor).

beltsander rewired

Still puzzling how such a nice machine can be made for so little money… the motor alone – just rewiring it takes the better part of 1 hour…. all nicely wrapped.

beltsander wire wrap

The capacitor, a CBB60 grade, 250 V, PP metallized capacitor. 12 µF.

beltsander ccb60 12uf capacitor

Finally, the belt sander assembled again – and ready for 230 VAC.

beltsander assembled

Some consideration of belt speed – the sander has a 95 mm diameter drive roll. A 60 Hz 2 pole induction cage capacitor motor will have about 3300-3400 RPM at full speed – that’s about 16 m/s grinding speed – OK for most materials (you might want to go a little faster on steel, and slower for touch-up and last steps of sharpening of knives, and similar objects).
Running at 50 Hz will reduce the speed to 13-14 m/s, fair enough.

115 to 230 vac rewiringbelt sanderharbor freightmotor rewiringpermanent split capacitor motor

Various

2016/04/17 Simon Leave a comment

With all the various HP power meters for repair, it would be really handy to have a range calibrator, HP Agilent Keysight 11683A. These have been around for 40+ years – any still not easy to find at any reasonble price – even used and non-calibrated units may be as much as 500 to 1000 USD. You can still buy it new:

11683a range calibrator

The internals, check out the picture provided by Keysight – there is a modified 8481a power head (using the same FET chopper assembly), a range switch using high quality 140 series Micro-Ohm non-inductive wire-wound resistors (0.1%, +-10 ppm temperature coefficient).

11683a internals

11683 schematic

Note that the schematic shows the H01 option – which allows an external DC connection, from a calibrated DC source. This is much preferred over the build-in power supply and resistive divider (which has known issues at low output voltages). The design of the 11683a also has some ground loop issues, better to just leave it disconnected from mains, and supply the DC voltage from a known-good source.

11683a calibrator instrument

These issues are known to the experts of the field, see, e.g., this comment from the Keysight EPM-P power meter manual.

11683a accuracy

Now, a very complicated issues with the range calibrator – it’s output isn’t strictly linear over the dB range, because the power meters have a shaping circuit, to compensate for the somewhat high output of the 8481A and similar sensors, above about 5 dBm of input power. Accordingly, the sensitivity is reduced for this range.

11683a 436a pwr meter high input signal adjustment

Furthermore, the 11683a has ranges labelled in mW, e.g., 3 mW, but the output actually is calibrated in 5 dB steps…. so the output power is more like 3.16 mW, etc.
To figure this all out, a thorough calculation has been done, considering the FET input impedance, the resistive network, and the range switch.

11683 nominal output

11683 dc calibrator input

At the 10 mW and 100 mW ranges, calibrations applied in the 11683A (and the 43x series power meters) were determined to be different from the newer EPM-P meters – quite surprising. The reason for this difference of the older meters, to the new EPM-P meters is rather hard to guess, but thanks to a kind engineer at Keysight, we now know: the EPM-P meter reacts differently to the 11683A (because it measures in virtually one range), in contrast to the 43x series meters that have several ranges. So, there is no difference in the actual power meter calibration, it is just a difference needed when considering using the 11683A for either 43x or EPM-P meters, because of the different response to the level calibration, but not actually different response to the power head when measuring actual RF power.

11683 correction

This table has the voltages that should be provided to the calibrator, depending what you want to do – (1) calibrate a EPM-P meter, (2) calibrate a meter “simulating” the acutal 11638A range switch voltages, (3) calibrate an old 43x power meter, with corresponding scaling factors for 10 mW and 100 mW ranges.

11683a ideal voltages

A quick scheme of the 11683A power supply, and the clear-written resistor values, which are not so clearly seen in some of the schematic copies.

11683 pwr supply

Now, how to get a 11683A range calibrator at reasonable cost? Turns out, you can build your own from one of the many defective 8481A that are around in most labs, and on xbay. Well, in fact, most “working” powerheads sold only for below USD 100 are dead anyway… but this is different story. These powerheads hardly ever have any issue with the copper and FET boards, but in most cases, the thermistor is dead, blown by too much input power.

11683 436a voltage check

The modification – a wire has to be added to connect signal and guard ground (brown wire), and a 196 ohms resistor soldered over the FET input (I used a 220 ohm resistor for the test, but will replace one 196 ohm on hand). Also, you need to add a 196k resistor to the input, according to the 11638A schematic (this can be assembled from some other resistors, if no 196k in stock).

11683 8481a modification

Make sure not to bend the wires – this can affect the FET chopper balance (see 8481A or 11683A service manual to re-adjust if needed).

11683 8481a board

The input is currently still arranged with open wires, but I will fit a 1n feedthrough cap soon – will modify the original N-connector (the golden part holding it). But this will need to be done back at the main workshop in Germany – need to use a lathe for it.

8481a n conx disassembled

Some test results will follow soon – but so far, everything is working just fine.

11683A43xEPM-PH01 optionpower meterpower meter calibrationrange calibrator

Various

2016/04/07 Simon Leave a comment

One of the products that have been in the HP/Agilent/Keysight catalog for 3 or 4 decades, or more, the 11708A reference attenuator. Specified at +-0.05 dB, it is a remarkably simple device – it just provides 1:1000 attenuation, chiefly, 30 dB. It’s main application is the calibration of 8484A power sensors, from a 1 mW source – the 8484A needs a 1 µW reference level.

Unfortunately, it doesn’t come cheap, when ordered from Keysight today, at least for a hobbyist’s budget. So I got mine used, aged (30 years?), and at a minor fraction of the cost.

11708a keysight

Before using it for a considerable number of power measurements, it is a good idea to confirm it’s performance. Measuring attenuation to +-0.05 or better is no easy tasks, but fortunately enough, a tractable one, with a 8642A signal generator, and a Micro-Tel 1295 precision attenuation measurement receiver. The Micro-Tel is specified to +-0.02 dB, plus +-0.02 dB for each 10 dB, say, +-0.08 dB. Actual performance, of a well-calibrated and well-heated-up unit is considerably better, but only in combination of other high quality components, like, a stable source (the 8642A has virtually no measurable drift), and, good test cables (using Suhner Sucoflex).

The Micro-Tel 1295 employs IF substitution to determine attenuation, and the IF attenuator works in 10 dB steps. Therefore, for best accuracy, the tests should be done at various power levels, to use various combinations of x0 dB segments, of the IF attenuator.

The results, quite remarkable!

11708a low level

11708a low level2

11708a high level2

One thing to consider for the test – the input and output matching losses. Neiter the source nor the cable/receiver are perfect 50 Ohm terminations – but the 6 dB pads will ensure only very minor losses. Obviously, you need to use high quality pads here, specified to small return loss, 18 GHz parts preferred.

First step – reference measurement is taken without the attenuator-under-test:

11708a test atten 1

Second step – actual measurement is taken with the attenuator-under-test installed between the two 6 dB pads:

11708a test atten 2

Before the start – best to check reproducibility and repeatability. With good cables and hardware, +-0.005 to +0.01 is achievable with the current setup.

Well, let’s say, chances are that the 11708A is +-0.02 off its nominal value, most likely, it didn’t drift at all over the last 30 years.

11708a30 dB reference attenuatorMicro-Tel 1295reference attenuator

Time Interval Counter

2016/04/05 Simon 1 Comment

A time interval counter – this little device, based on an Atmel AVR ATMega32L assigns 64 bit time-stamps to events (event being a rising edge on INT1 interrupt), based on a 10 MHz OCXO, a Trimble 65256 10 MHz double oven oscillator. So, 100 ns resolution. The main purpose: precise monitoring of pendulum clocks – in combination with a temperature-air pressure-real time clock data logger.

Why TIC4 – well, there are several other (earlier designs), some with better resultion by interpolation (via a clock synchronizer and interpolation circuit). But for the given purpose, there is no need for any more than a few microseconds of resolution, because it is really hard to detect the zero-crossing of a mechnical pendulum to any better resolution.

For test purposes, I had the circuit running on a 16 MHz clock, with ordinary (not very precise or phase locked) 20 Hz, and 2 Hz signals at the input – running overnight to check for any glitches.

tic4 allan dev 50 ms

tic4 allan dev 500 ms

The Allen deviation plots show that for single events, the timing accuracy is about 150-200 ns, close to what is theoretically possible for a 16 MHz clock.

The AVR program code, it looks simple, but believe me, it isn’t. There are quite a few pitfalls, because for any timing of the interrupt, there needs to be a precise time-stamp generated, and transmitted to the host. Maximum time stamp rate is 100 Hz nominal (1 timestamp every 10 ms), but will work up to about 150 Hz, without missing any events. Timestamps are transmitted with every 16 bit timer overflow, chiefly, every about 6.6 ms (65535 x 100ns). Each timestamp and control info is 120 bit long (12 bytes, 8N1 protocol, 57600 baud) – 2.1 ms.

tic4.c AVR code

For test purposes, the serial data is sent to a PC, via a MAX3232 TTL to RS232 converter. Alavar is used to process the information into Allan deviation plots.
Test showed absolutely no glitch in about 1.3 million events – fair enough!

More details to follow.

TIC4Time Interval Counter

Miscellaneous

2016/04/04 Simon Leave a comment

This is a good, fast and simple wheat bread. Optimized for baking in gas-fired ovens.

1600 g wheat flour (1:1 mix of ordinary and bread flour; up to about 300 g wholewheat flour is OK)
30 g salt
1 package dry yeast

Dry-mix thoroughly.

Add 1200 mL of warm water.

Mix/knead. Let rise thoroughly. Knead again – add some flour as needed.

Form elongated shape breads. Let rise.

Bake in pre-heated oven to 425 F. For best result, add water in tray at start of baking.

ordinary wheat bread

wheat bread

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