HP 85685A: another mains filter failure – Schaffner FN 376

With the 85685A repair complete, the instrument was subject the an extensive test, to make sure all is in good order and working stable. Well, it did work well for a while, then – PUFF! The mains filter blew, one of the infamous Schaffner filters that is designed to blow up after about 20 years of service. Schaffner is one of the only companies I stay away from for any design – it is a Swiss enterprise, but too many of their devices failed in my hands – their filters are often the first parts to fail, in high grade test equipment.

The 85685A, like most other HP gear, has the mains filter combined with a voltage selector switch.

Cutting it open, you can see the Wima MP3 cap, 47 nF, 250 VAC. The MP3 are metallized paper capacitors, rated for X2 (mains) service. All embedded in some black resin.

Copper wires of the choke showing trough.

New filters that match the FN 376 are hard to find, and new-old-stock, well, these filters might fail again. So I decided to go for a new filter, a Schaffner-free solution.

This will be the new filter – a ID-10AC-S, available for little money, and seem to be pretty good for their current rating.

The internals… the filter elements are nicely encapsuled in a two-shell plastic case. No potting compound!

The X2 capacitor, and the choke…

Transplanted to the Schaffner filter body… and wrapped with Cu tape, soldered closed, for EMI shielding. All well grounded!

From the datasheets, you these filter should have 20-30 dB loss at 1 MHz. Let’s put it to a test!

For the new assembly, tested with a 3585A, about 12 dB loss at 100 kHz, 30 dB loss at 1 MHz, should be good, and no modification necessary to the 85685A.

HP 85685A Preselector Repair: faulty attenuation

The HP/Agilent/Keysight 85685A Preselector is a great addition to any 8566B or 8568B spectrum analyzer. The preselector converts the analyzer into a test receiver, by increasing its dynamic range by 30 dB, down to very low noise levels.

Recently, I got a 85685A for repair, only knowing that it doesn’t work as it should. With some checks, it was very quickly evident that there must be a issue with the RF attenuator, or its driver.

This defect is clearly seen when looking at a test signal at various attenuation levels of the 85685A. The signal should stay at the same level, irrespective of the attenuator setting, but as soon as you go from 10 dB to 20 dB, the signal vanishes almost completely. This is not good.

This is the RF attenuator, a Wavetek OEM part. Unfortunately, there is no service manual for the 85685A available, so we need to figure it out by ourselves.

First, determined the switch matrix for the attenuator controls, by probing the control inputs at various attenuation settings. Pretty clear, there are 10 dB – 5 dB – 20 dB – 20 dB segments inside, which are activated by pulling the respective control input low. Easy enough.

After some disassembly of the case (removing the rear panel), you can get access to the four screws holding the attenuator to the case.
Notably, the case of the 85685A uses Torx screws, unlike most other HP equipment using this style of enclosure.

Underneath the label, there is now hidden screw to get to the internals of the attenuator, all is glued closed and sealed with silver epoxy. To break it open without destruction, I milled a small slot from the side of the unit. Probably could have milled a bit shallower, and a bit less, but OK.

With the slot, the lid is easily removed using a screw driver. Make sure not to bend the lid too much.

Looking inside, it is pretty obvious that someone must have fired a lot of power into the unit, when set a 20 dB input attenuation. Checked all other segments with a 8752A network analyzer, and all good, except for one of the 20 dB segments, as expected.

How does a 20 dB attenuator work? There are several topologies, Wavetek used a so call pi-arrangement of resistors. Only two of the resistors are blown, the output resistor is OK (this is also clear from the fact that most power is dissipated in the left two resistors).

The switching of the attenuator segments is done with miniature RF relais, similar to these. At over EUR 40 a piece – glad these are all good.

The relais are DPDT switches, soldered flush to the board (which is a PTFE composite board), for best RF performance.

For repair, we need to replace the resistors with good new parts – but there are hard to come by, with not even a Wavetek datasheet available for the attenuator, let alone, these parts.

Several attempts were made to get the best (lowest) SWR, and the best flatness, at very close to 20 dB attenuation.

First, used a combination of 1206 SMD resistors to get close to the values needed.

This is the flatness of the “good” 20 dB segment:

This is the flatness of the “1206 repaired” 20 dB segment:

Another style of repair, with the same parts, now soldered directly between the legs of the relais:

… no improvement, still quite some reduction of attenuation above 2 GHz.

Now, tried with a series arrangement of 0805 resistors for the 250 Ohm resistor (giving lower stray capacitance).

… quite some improvement!

Red is the good attenuator section, blue is the repaired section, at 0.2 dB/div scale!

I would call it good enough!

A quick SWR test (non-calibrated) for “through” and “actuated” setting of the repaired segment (and terminated in a 15 dB precision 18 GHz rated attenuator at the output) showed low SWR (keep in mind, the 85685A will only work up to 2 GHz anyway).

All sealed up with silver epoxy – a bit old stuff around here, but still working. And, used some Cu tape (with conductive glue, 3M type 3313), to make sure all is sealed well and forever.

Now, with the attenuator fixed and working, one more thing to consider – the power handling capacity. The 85685A is rated for up to 30 dBm (1 Watt) average power. Not sure if the SMD resistors used can handle it – they are a bit smaller than the original Wavetek parts. So I decided to swap the control lines for the two 20 dB segments. This way, the “good”=Wavetek segment No. 3 will always take most of the power, and the repaired section (SMD resistors) will only be needed for the highest attenuations, and never see any more than 10 dBm of power, even at the maximum allowable input. Still, I will keep a search going on a spare 0955-0235 programmable attenuator, for a reasonable price (some of these being offered for USD 100, which is a bit more than I want to spend for a 25 year old part of unknown nature and condition).

Finally, all assembled back together, and performed a flatness/attenuator test, by supplying a signal at -40 dBm from a 8642B generator. Measured amplitude at 1 kHz resolution BW is pretty flat over all attenuator settings and frequencies.

Let me know in case you have any 85685A units for repair….

Chair Repair: build in 1991, refurbished in 2017

My good old office chair has seen better days, with permanent use sind 1991, during all my study and overseas activities. At least, it is not a cheap imported chair, but a good old German made and top quality office chair, purchased for about 300 Deutschmarks in 1991. A very generous gift of my parents, who took care of my back even at those early days.
But now, all the fabric is work, and even holes showing up, and threads loose.

Sure, there are many professional repair shops that can do a full overhaul of such chairs, but what about the do-it-yourself spirit? So I decided to fix it myself, using simple tools, like, a nail gun (see below), a razorblade, some fabric (corduroy, available from a local shop at low cost), and a fleece (non-woven, anti-slip impregnated) fabric (about 100 g/m2 weight).

This is the nail gun I use, a Ferm ATM1042. It’s quite sturdy, and a great deal for the price!

The nails used are 5.8×13 mm, quite easy to worth with, using an air-pressure operated gun.

The fleece serves an important purpose, it covers the old fabric (nothing removed from the chair), and gives it some new firm touch. And, because of its anti-friction properties, it will not slip between the old and new fabric. And, it is available locally, at low cost. I used a single layer for the back rest, and two layers for the seat, cut to size.

Here you can see progress on the back-rest. Make sure the fabric is aligned property, then first fix two opposite sides with the needle gun. Then, continue with the perpendicular sides, then diagonally, and so on. Always apply an even “pull” to make sure the fabric looks nicely stretched around the corners. Avoid any wrinkles by pulling the fabric straight, and by applying more nails from the gun. After all, don’t safe on nails!

For the seating surface – the same procedure.

Voila, all done, and ready for at least 10 more years of service!

Manuals Additions: Motorola!

Thanks to a kind contributor, Mike, about 230 Motorola manuals have found there way into to archive. Included are various detail manuals and service guides of the GP series, and other quite popular Motorola radios.

Happy to receive any of your manual collections related to test equipment, high frequency electronics, or related fields. Will keep them online free of charge for everyone, and all well backed up.

motorola
| |– [8.7M]  6864115B18-D GP300 Basic Service Manual.pdf
| |– [421K]  AP-73 user manual.pdf
| |– [2.4M]  Astro Digital Spectra _ Digital Spectra Plus Basic service manual.pdf
| |– [3.3M]  ASTRO Saber Basic Service manual DigitalPort.pdf
| |– [1.6M]  Astro service software user guide.pdf
| |– [7.5M]  Astro XTL5000 basic service manual.pdf
| |– [1.9M]  Astro XTL5000 Detailed User Guide.pdf
| |– [7.9M]  ASTRO® XTSâ„¢ 2500 user guide.pdf
| |– [897K]  BPR_40.pdf
| |– [7.0M]  Business Portable Radio service manual.pdf
| |– [363K]  Business Portable Radio user guide.pdf
| |– [1.8M]  CDM and PRO SERIES detailed service manual.pdf
| |– [2.5M]  CDM Series Basic Service Manual.pdf
| |– [8.4M]  CDM Series Control Station Service and Installation Manual.pdf
| |– [2.3M]  CEP400 basic user guide.pdf
| |– [6.2M]  CM140 basic user guide.pdf
| |– [1.3M]  CM140 CM160 service manual.pdf
| |– [491K]  CM160 user guide.pdf
| |– [3.8M]  CM200 CM300 PM400 basic service manual.pdf
| |– [8.7M]  cm200 cm300 pm400 detailed service manual.pdf
| |– [351K]  CM340 user guide.pdf
| |– [523K]  CM360 User Guide.pdf
| |– [2.3M]  CM Radios Detailled service manuals.pdf
| |– [1.3M]  Commercial Series CM service information.pdf
| |– [160K]  CP140_160.pdf
| |– [8.4M]  cp150 cp200 detailed service manual.pdf
| |– [5.5M]  CP185 Service Manual.pdf
| |– [8.4M]  CP200 Detailed service Manual.pdf
| |– [7.0M]  Digital XTS 3000TM full featured model user_s guide.pdf
| |– [5.3M]  Digital XTS 3000 user guide.pdf
| |– [8.1M]  disney2wayadv user manual.pdf
| |– [3.9M]  DM 3400 user guide.pdf
| |– [1.1M]  DM4400 user guide.pdf
| |– [1.2M]  DM4600 user guide.pdf
| |– [7.2M]  DP 3400 user guide.pdf
| |– [8.4M]  DR 3000 basic service manual.pdf
| |– [8.4M]  DR3000 MOTOTRBO Repeater basic manual.pdf
| |– [6.9M]  DR3000 MOTOTRBO Repeater basic service manual.pdf
| |– [9.0M]  DR3000.pdf
| |– [ 79K]  Emergency Foot Switch instruction manual.pdf
| |– [5.2M]  EP450 basic service manual.pdf
| |– [1.5M]  EP450 detailled service manual.pdf
| |– [ 63K]  Flashing Adapter HLN9742 Service Manual.pdf
| |– [345K]  FLASHport user guide.pdf
| |– [4.0K]  GM1200E detailled service manual
| | |– [1.6M]  dsm_a3s.pdf
| | |– [249K]  dsm_a4s.pdf
| | `– [924K]  GM1200E_SM _EN.pdf
| |– [924K]  GM1200E service manual.pdf
| |– [326K]  GM1200_UG_EN.pdf
| |– [889K]  GM1280 user manual.pdf
| |– [1.4M]  GM300 basic service manual.pdf
| |– [808K]  GM300 service manual (3 parts).pdf
| |– [ 14M]  GM300 service manual.pdf
| |– [217K]  GM340 user guide.pdf
| |– [4.0K]  GM350 installation manual
| | |– [440K]  350IN_EN.pdf
| | |– [ 25K]  350RS_EN.pdf
| | |– [ 74K]  350ug_en.pdf
| | `– [119K]  950rmkit.pdf
| |– [561K]  GM360 user guide.pdf
| |– [692K]  GM380 user guide.pdf
| |– [722K]  GM-660_Manual.pdf
| |– [871K]  GM series Radio Installation manual _ service manual.pdf
| |– [119K]  GM Series service information.pdf
| |– [3.3M]  GP1280 basic service manual.pdf
| |– [1.9M]  GP1280 user guide.pdf
| |– [4.0M]  GP300 Basic service manual.pdf
| |– [231K]  GP300 Service manual (schematics).pdf
| |– [1.9M]  GP320 user guide.pdf
| |– [8.4M]  GP328 GP338 Detailed service manual.pdf
| |– [8.1M]  GP328 Plus detailed service manual.pdf
| |– [453K]  GP328plus GP338plus GP338XLS Basic service manual.pdf
| |– [8.1M]  GP328plus GP338plus GP338XLS detailed service manual.pdf
| |– [4.1M]  GP330 user guide.pdf
| |– [1.9M]  GP340 Ex Portable Radio basic user guide.pdf
| |– [2.2M]  GP340 user guide.pdf
| |– [257K]  GP344 user guide.pdf
| |– [3.4M]  GP350 service manual.pdf
| |– [4.0K]  GP350 User Guide
| | |– [374K]  gp350_part1.pdf
| | |– [1.5M]  gp350_part2.pdf
| | `– [703K]  gp350_part3.pdf
| |– [1.8M]  GP360 user guide.pdf
| |– [2.8M]  GP380 Ex Portable Radio basic user guide.pdf
| |– [1.9M]  GP-380_Manual.pdf
| |– [1.2M]  GP388 user guide.pdf
| |– [4.4M]  GP580 Ex Portable Radio basic user guide.pdf
| |– [4.0M]  GP600 series Basic Service manual.pdf
| |– [2.2M]  GP640 GP680 Basic Service manual.pdf
| |– [1.8M]  GP640 GP680 Basic User Service manual.pdf
| |– [2.2M]  GP-680_Manual.pdf
| |– [1.3M]  GP68 User Guide.pdf
| |– [4.0K]  GP Series detailed service manual
| | |– [384K]  B32E_Sect1_Service Maint.pdf
| | |– [518K]  B32E_Sect2_Keypad_A3.pdf
| | |– [ 89K]  B32E_Sect2_Keypad_A4.pdf
| | |– [576K]  B32E_Sect3_Controller_A3.pdf
| | |– [210K]  B32E_Sect3_Controller_A4.pdf
| | |– [2.6M]  B32E_Sect4_VHF_A3.pdf
| | |– [255K]  Chap 1 Introduction_A4_v0.pdf
| | |– [234K]  Chap 2 Theory of Operation_A4_v0.pdf
| | |– [718K]  Chap 3 Maintenance_A4_v0.pdf
| | |– [551K]  Chap 4a Controller and Keyboard Info_A3_v0.pdf
| | |– [240K]  Chap 4a Controller and Keyboard Info_A4_v0.pdf
| | |– [525K]  Chap 4b VHF Info_A3_v0.pdf
| | |– [510K]  Chap 4c UHF1 Info_A3_v0.pdf
| | `– [511K]  Chap 4d UHF2 Info_A3_v0.pdf
| |– [9.3M]  GR300 GR500 service manual.pdf
| |– [2.3M]  GTX LCS 2000 service manual.pdf
| |– [968K]  HF-SSB Automatic Antenna Tuner owner_s manual.pdf
| |– [573K]  HKLN4197A_PRO2150_Eng.pdf
| |– [9.3M]  HT1000 JT1000 MT2000 MTS2000 MTX series Service manual.pdf
| |– [477K]  HT1000 MT2000 MTS2000 MTX series Service manual.pdf
| |– [4.3M]  HT1250 user guide.pdf
| |– [4.9M]  HT750 HT1250 MTX850 MTX1250 MTX8250 MTX9250 basic service manual.pdf
| |– [1.9M]  HT750 HT1250 MTX850 MTX1250 MTX8250 MTX9250 supplement basic service manual.pdf
| |– [ 12M]  HT800 VHF service manual.pdf
| |– [3.0M]  HT90 service manual.pdf
| |– [2.2M]  HT Series detailed service Manual.pdf
| |– [2.2M]  LCS2000 service manual.pdf
| |– [1.4M]  LTS 2000 user_s guide.pdf
| |– [6.9M]  Mag One basic service manual.pdf
| |– [1.7M]  MagOne Basic Service manual.pdf
| |– [433K]  Mag One BPR40 Brochure.pdf
| |– [4.8M]  MagOne detailled service manual.pdf
| |– [2.1M]  MCS 2000 Mobile Radio.pdf
| |– [295K]  MCS 2000 Model I User Guide.pdf
| |– [306K]  MCS 2000 Models II _ III user manual.pdf
| |– [2.1M]  MCS2000 service manual vol-1.pdf
| |– [1.1M]  MCS2000 service manual vol-2.pdf
| |– [1.3M]  MICOM-2E ALE owner_s guide.pdf
| |– [ 36M]  motorola gm 900_sm.pdf
| |– [533K]  MOTOROLA KIT HSN4035 Service Instruction.pdf
| |– [647K]  motorola Models T4800 T4900 Instruction.pdf
| |– [1.2M]  motorola Models T5600 T5620 T5700 T5710 T5720 instruction.pdf
| |– [1.4M]  motorola Models T5800 and T5820 instruction.pdf
| |– [1.0M]  motorola Models T5900 T5920 and T5950 instruction.pdf
| |– [ 38M]  motorola mototrbo dp3400 3401 3600 3601 sm.pdf
| |– [101K]  Motorola NMN6250 NMN6251 – service manual.pdf
| |– [7.0M]  motorola_novacommunications_business_portable_radio_cp125.pdf
| |– [7.0M]  motorola_nova_cp125_sm.pdf
| |– [372K]  Motorola P040 P080 Controller – schematics.pdf
| |– [533K]  Motorola P040 P080 UHF – schematics.pdf
| |– [772K]  Motorola P040 P080 VHF – schematics.pdf
| |– [1.5M]  Motorola P200 – operating instructions.pdf
| |– [1.5M]  Motorola PRO3100 UHF – schematics.pdf
| |– [2.3M]  Motorola PRO3100 VHF – schematics.pdf
| |– [2.3M]  Motorola PRO5150 – schematics.pdf
| |– [196K]  Motorola Systems Saber – UHF specifications, service manual.pdf
| |– [196K]  Motorola Systems Saber – VHF specifications, service manual.pdf
| |– [387K]  Motorola T4502 – instruction manual.pdf
| |– [3.5M]  Motorola T4512 – instruction manual.pdf
| |– [4.2M]  Motorola T5022 – User.pdf
| |– [3.2M]  motorola T6200 T6210 and T6220 instruction.pdf
| |– [5.2M]  Motorola XTL1500 users guide.pdf
| |– [2.2M]  Motorola XTL2500 users guide.pdf
| |– [9.7M]  Motorola XTS4000 basic service manual.pdf
| |– [6.0M]  Motorola XTS4000 detailed_service_manual.pdf
| |– [3.0M]  Motorola XTS4000 user service manual.pdf
| |– [3.6M]  Motorola XTS4250 – advanced model user guide.pdf
| |– [2.7M]  Motorola XTS4250 user guide.pdf
| |– [2.0M]  Motorola XTS5000 parts list.pdf
| |– [ 34K]  Motorola XTS5000 service aid sheet.pdf
| |– [5.2M]  Motorola XTS5000 user guide.pdf
| |– [5.7M]  MOTOTRBO DR3000 Repeater basic service manual.pdf
| |– [516K]  M-Series Owner_s manual.pdf
| |– [1.6M]  MSF 5000 maintenance and alignment manual.pdf
| |– [ 44M]  MSR2000 Control _ audio operation _ service manual.pdf
| |– [ 37M]  MSR2000 operation and service manual.pdf
| |– [8.3M]  MT1500 basic service manual.pdf
| |– [1.9M]  MTH500 Basic Service Manual.pdf
| |– [4.0M]  MTH500 Tetra Detailed Service Manual.pdf
| |– [1.2M]  MTH650 Tetra Basic User Guide.pdf
| |– [3.3M]  MTH800 TETRA basic service manual.pdf
| |– [4.3M]  MTH800 TETRA basic user guid.pdf
| |– [5.8M]  MTP700 Detailed Service Manual.pdf
| |– [2.1M]  MTP810 Ex TETRA basic service manual.pdf
| |– [2.1M]  MTP850 EX Basic Service Manual.pdf
| |– [8.4M]  MTP850 TETRA basic service manual.pdf
| |– [2.2M]  MTX Series detailed service Manual.pdf
| |– [3.8M]  MX300-S series service manual.pdf
| |– [4.0K]  p040-080_all_man
| | |– [1.9M]  10B67_UG.pdf
| | |– [2.3M]  10B68_UG.pdf
| | |– [163K]  13B29_CPS.pdf
| | |– [926K]  14B36_SG.pdf
| | |– [4.5M]  15B49_BSM.pdf
| | `– [ 40K]  ENLN4122A.pdf
| |– [2.7M]  PM400 Basic Service Manual.pdf
| |– [ 11M]  PM400 Detailed Service Manual.pdf
| |– [3.7M]  PR400 Basic Service Manual.pdf
| |– [9.5M]  PR400 Detailed Service Manual.pdf
| |– [1.8M]  PRO Series detailed service Manual.pdf
| |– [2.3M]  R-1011B Instruction manual.pdf
| |– [392K]  R-1013A operation _ service manual.pdf
| |– [6.9M]  R-1100A Operation manual.pdf
| |– [1.4M]  R-1150 R-1151 operation manual.pdf
| |– [2.5M]  R-2008C Operations manual.pdf
| |– [ 48M]  R-2200A service manual.pdf
| |– [3.5M]  R-2200 R-2400 operation manual.pdf
| |– [3.6M]  R-2600 SERIES Operator manual.pdf
| |– [1.0M]  Radius CM200 installation guide.pdf
| |– [769K]  Radius M100 M200 Owner_s manual.pdf
| |– [3.5M]  RLN-4008B service manual.pdf
| |– [2.7M]  S1051C S1053C operation _ service manual.pdf
| |– [4.4M]  S1067A operation and service Manual.pdf
| |– [ 12M]  S1318A S1319A S1320A S1321A S1329A operation _ service manual.pdf
| |– [267K]  SABER Portable Radios user_s guide.pdf
| |– [191K]  SABER Theory _ Maintenance manual.pdf
| |– [1.3M]  SM_GP68.pdf
| |– [3.9M]  Spectra Conventional Radio System Operating Instructions.pdf
| |– [458K]  Spectra Privacy Plus Operating Instructions.pdf
| |– [573K]  Spirit GT Operator_s manual.pdf
| |– [3.6M]  SSE 5000 service manual.pdf
| |– [8.4M]  Syntor X Maintenance and troubleshooting manual.pdf
| |– [3.3M]  TETRA MTH800 basic service manual.pdf
| |– [1.7M]  TETRA MTP850 basic service manual.pdf
| |– [ 10M]  XPR7000 basic service manual.pdf
| |– [ 11M]  XPR 7000 Seris basic service manual.pdf
| |– [4.0K]  XTL5000
| | |– [2.0M]  96C67-C_AX_UG_XTL5000_W3.pdf
| | |– [1.9M]  96C68-D_AX_UG_XTL5000_W4579.pdf
| | |– [3.2M]  98C38-O_v4.pdf
| | `– [622K]  9964416H03_O_XTL5000_AT_IM_Dual-Radio_CH.pdf
| |– [6.2M]  XTS1500 XTS2500 basic service manual.pdf
| |– [698K]  XTS3000 parts list.pdf
| |– [698K]  XTS3000 XTS3500 parts list.pdf
| `– [625K]  ZR310 service manual.pdf

Rigol DS1052D=DS1102D Oscilloscope: encode issue fix

For about 8 years, I have been using a Rigol DS1052D 50 MHz scope (which works up to 100 MHz with a well known software fix), but recently, it has given me some grieve: the knobs turn, but the settings jump, both for scale and time base. This is quite annoying – trying to fix something, with broken tools or scopes, is no fun.

Already expecting the worst, like, mechanical failures of the scope of encoders, or some strange software bug (because all encoders were affected at virtually the same time), I decided to open up the scope. Easier said then done. There are 4 screws, two of which are under the handle, and you have to remove the powder on button with some bent wire (don’t scratch the case!). Then, move around the back cover, eventually, it will come off! Don’t give up! Don’t remove the screws of the power input socket!

Once inside, you need to take off the two screws for the D9 connector, and then, several more screws to take out the power supply, before you finally get to even further screws holding on the front panel.

Before taking any soldering iron to replace the encoders, as suggested by some folks on google, I tried to use the magic DeoxIt D5 to clean up things and to get it going again. Just spray some of the stuff into the encoders, there are some small openings (circled red on in the image). Turn the encoders to make it work. After a while, clean of any excess D5, don’t let it get in touch with the rubber of the DS1052D buttons – most rubber can handle D5, but better not try your luck!

And, it worked like magic. Not only are the encoders working again, but also the feel of the knobs is much better, not as sticky as it used to be.

Xmas Cookies: Heidesand

It’s never to early to prepare for Xmas, and certainly not too early to bake some cookies anyway.

These cookies are a specialty of our family, called “Heidesand”, but it is a modified recipe, and a bit different compared to the Northern German original.

For the dough, thoroughly mix and knead:

250 g butter (soft)
100 g finely powdered sugar
100 g marzipan paste
300 g wheat flour type 405

The dough will be rather soft after some kneading, but don’t worry!

Form to rods of about 1″ diameter, wrap in aluminum foil and let cool/solidify in the fridge overnight.

Cover with some egg jog, and roll in sugar to fully cover the outside with crystals.

Immediately cut in slices, about 3/8 of an inch thick. Put on non-stick paper with a good distance between the slices. Don’t let the rolls warm up! For best results, only cover one roll with the sugar coating at a time, and cut it into slices, before proceeding with the next roll.

Bake at 175°C, circulating air oven, for about 11 minutes (perimeter of the cookies must be brown, inside only lightly colored).

Everything done right – the cookies will look like this, and taste even better:

A wireless door bell, activated by a wired door bell!

Winter time, is workshop time, spending several hours in the workshop every week, either in the ground floor workshop, or basement rooms – and on several instances, missed the postman! Especially on Saturday, when nobody else is at home, an I am waiting for some spare parts!

The simple reason, the door bell only rings in the office/apartment on the 3rd floor, but I can’t hear it in any of the workshops. This needs to be solved – but how? Running a wire through several floors is no option.

Browsing through online offers, I found some low-cost wireless doorbells (120 meters range!! probably, Chinese meters but fair enough) and came up with this scheme – the 3rd floor apartment door bell, which is integrated into a Siedle-brand HT411 door phone will trigger the transmitter of the wireless door bell, which in turn will give its sound in the workshop are.

This is the xbay offer – one transmitter, and two receivers.

That’s the HT411 with the transmitter mounted.

The door bell uses a transformer-less powder supply… let’s hope it will last.

Finally, the simple schematic using the “ring” signal of the HT411, which is 12 VAC to activate the door bell transmitter (with the button shorted, it will activate the received whenever power is applied!).

All is working loud and clear now, you push the main door button, then the HT411 will ring in the apartment 3rd floor, this in turn will active the wireless transmitter, and both receivers will sound in the 1st and basement workshop. Easy enough!

Holzmann BS 128HDR: “Holz” means wood, but this is a metal band saw!

For several years, I have been using hacksaws and similar tools, and other less suitable and dangerous tools to cut-off metal stock for milling and turning. Or, I used some friends’ equipment, which is troublesome and time-consuming – to travel to far-away places just to cut some metal.

With the space I have in the basement, there is no room to fit a large industrial band saw, and I wanted to get a machine that can also cut at an angle, for some welding and fabrication work. The machine selected, a Holzmann BS 128HDR is one of the common Chinese designs, but these are not all made equal, and the Holzmann looks like a good brand. Cutting capability is 125 mm diameter round, 100×150 mm square, which should be good for 99% of the work.

All came in two boxes, on a wooden pallet.

Some tests with 42CrMo4, and 26CrMo4 rod. It is cutting perfectly fine. Also checked with some square tubing, which can be challenging for some cheap band saws because of the thin-walled sections, but the 128HDR has a hydraulic break/mechanism, which provides smooth cutting action even for these more difficult materials.

For lubrication, you can use any type of ordinary oil, HLP 68 hydraulic oil works well and is cheap, with no smell.

Historic view of the workshop – Joh. Eisele Porzellan Grosshandel, Ludwigshafen

Found this great view of the current workshop (ground floor, left windows), dating back to before 1918! The building itself dates back to 1910, established by Joh. Eisele, who used to operate a major trading house for porcelain, glass, and stone ware, including a decoration workshop for such items.

While the back factory (with the railway tracks) is missing today (maybe bombed out it WW II?), the main building still exists today, in quite recognizable shape and form, even still with the name of Joh. Eisele in golden letters!

Micrometer and Force: a time-stamped interface

For a special application that I can’t name here, we need to measure both deflection (length) with about 0.01 mm resolution, and force in the range of 200 N (=20 kg). The force measurement is needed with a few 10s of Hz of temporal resolution, for deflection ~10 Hz will be sufficient.

All this needs to be accomplished at a budget, so I decided to use a China load cell (20 kg range), with an HX711 converter board, and a digital micrometer dial (13 mm range, 0.01 mm resolution).

First, to the HX711. As per the datasheet, it can be run from an external clock source, not sure if this is necessary, but thought I give it a try. Spec range for the clock is up to 20 MHz (normally running at about 11 MHz), but the HX711 works well to 70 MHz and above. You don’t need to couple a lot of power, even at -10 dBm, it is still working. Anyway, by setting the clock control pin to HI, the HX711 will provide a data rate of 80 Hz. As with all analog-digital converters, there will be a trade-off for frequency vs. noise-free resolution, but for the application discussed here, even 10 bit would be enough, to serve the purpose.

For the digital dial – unfortunately, the industry (the Chinese digital caliper and dial industry) has not yet come to a decision to use a commonly available connector to get the signal for a digital caliper or dial into a cable. At least, they offer various types of data protocols, and with not too much sense detective work, you can figure out how to interpret the data. I user a Micro-USB connector, carefully soldered to the data output pads of the micrometer dial.

Some small wires were used to connect the USB connector to the board, to allow for some movement, and to ensure longevity even in an environment that has vibration, and people connecting the USB cable with not much care.
The dial is running on 1.5 V (a single button cell), so we need a small converter board, using half of a MC3302P quad comparator, to convert the 1.5 V logic to good old 5 V TTL logic. You can use any type of comparator of logic conversion circuit, even a single transistor may work. Anyway, I didn’t want to load the dial any more than necessary, and to improve noise immunity, added a 20 MHz low-pass (330 Ohm with 22 pF) to the input.

Here the rising edges, logic conversion board input (blue), vs. output (yellow). For the faster traces, the internal pull-up resistors of the ATMega8 were enabled. Not much effect anyway.

All the data are collected by a ATMEGA8-16PU, and sent to a host PC via a 115.2k RS232 link. This allows even wireless connections, with a serial-to-RS232 converter. Data are send in one direction only, from the ATMEGA8 to the PC. All measurements have a 16 bit time stamp, using the ATMEGA8 16 bit timer.

The 8 bit timer of the ATMEGA8 is used to capture the data from the micrometer, which uses a synchronous clock to transmit data – the risking edge of the clock will trigger an interrupt, INT0, and the timer will ensure that each data Frame is received properly (the timer will overflow after each received data package, to signal that the next clock edge will be the start of a new data package).

The dial transmission pattern: one data block is send every ~100 ms.

Some detail of the timing, for the current dial indicator interface, data are valid at the rising edge of the clock.

For the last bit, there is no falling edge of the clock.

For “0” logic state, the dial interface pulls down the data line for each clock pulse, and then releases it again for high. Not sure why that is, maybe it saves some battery power?

The data is transmitted as binary number, 24 bit, 0.01 mm or 0.005″ per count. The last 4 bits are uses for status and indicate a “-” display, and mm vs. inch.

That’s the full pattern of a transmission sequence from the HX711. Blue is data, yellow is clock.

Timing – data line changes states quickly after the rising edge of the clock signal.

This is the final data stream as received. Notice the time-stamped load cell and dial transmissions.

For those interested, here is the MCU code (AVG-GCC): loadc_d0.c