Recent Posts

1

Projects, Designs, and Technical Stuff / Re: A naive question about automotive CANbus sniffing and spoofing

« Last post by uer166 on Today at 09:26:26 pm »

    But this isn't about getting rid of old cars that might generate more air pollution.  This is the auto makers designing their cars so that they CAN'T be repaired once their limited supply of (grossly overpriced) spare parts modules are sold out.  With the E serial numbers, it will be impossible to reuse modules from a wrecked car so the car owners will be 100% reliant on the auto makers for any replacement parts.  That's very bad news for anyone that wants to keep their car for more than a very limited number of years.  And it will also drive the price of spare parts (and car ownership) through the roof.   

   Ca-Ching$ for the auto dealers and manufacturers.

What an absolute load of crap.

1) The vast majority of ECMs are not locked down by SN with exception of maybe the immobilizer/security module.
2) The over-priceness of replacement parts is a choice. E.g. Tesla often sells them at or below cost. You end up with a situation where the main pyro fuse can be had for the price of lunch.
3) Service does not really make auto mfg money. Warranty costs billions so they'd rather the stuff be reliable in the first place.
4) The diagnostic tools of modern cars are so far ahead of years prior, the vehicle knows exactly what's wrong with itself like 80% of the time. Those tools are now more than ever available to end users and independent service centers for a fee.
5) The reliability of modern vehicles is orders of magnitude higher than anything from the 1980s/90s, in part due to computerization and modern control loops, negating need for any physical tuning. The overall $/mile is quite low as well.
6) As someone who lives in a big city, I am absolutely thankful there are no more small diesels, and something like ~30% of vehicles are now EVs. The externalities of shitty old cars cannot be overstated.

2

Metrology / Re: Experiments with Vref Ovens

« Last post by dietert1 on Today at 09:22:22 pm »

Yesterday i tested the experimental TEC oven driver shown in the image.
It has a Nucleo STM32L432 module, an ADS1256 ADC module, a linear power supply for the output stage with 4x IRF540 and a 0.235 Ohm shunt. The SIC473 buck converter adapts the supply voltage according to TEC output current, so the lower mosfets of the bridge stay cool and work in linear mode. The design TEC current is +/- 2 A.
The output stage is controlled by a DG4053 MUX for heat/cool switching and an OPA140. Hidden below the ADC module is another MUX for voltage reversal of the thermistor and its reference resistor (blue, 10K2, 5 ppm/K). Also there is a DAC8551 for TEC current control.
The thermometer with voltage reversal gives one measurement per second at a noise level of 10 uK (standard deviation). Noise of the resistance measurement is 0.4 ppm.
So i connected a little oven and implemented configurable PID control. Gains were adjusted by hand. They are pretty high and the first diagram shows the damped oscillation (47 s period). At steady state the effectve gain is less due to thermometer noise and TEC current digitization noise. The diagrams show temperature and TEC current logs at two different time scales. Oven temperature in °C in red and TEC current in A in blue. The oven and its heatsink are protected from air movement. During the last hour the oven temperature log exhibits a 11 uK standard deviation.
The thermometer circuit has unused channels, so one can also measure ambient or TEC heatsink temperature and/or use a second thermistor mounted on the oven lid.
Last image shows a similar four channel TEC output stage that i made for a LTFLU reference array. It has an OPA4140 and a DAC8554. There is only one buck converter as all four ovens run at similar temperatures.

Regards, Dieter

3

Test Equipment / Re: Cheap DSO153 (not 152) or DSO154Pro for measuring amp for clipping? please help

« Last post by Fungus on Today at 09:19:11 pm »

+1 for the Zeewei DSO154Pro

4

Test Equipment / Re: Siglent SDS800X HD Review & Demonstration Thread

« Last post by 2N3055 on Today at 09:19:06 pm »

SDS2000xHD 1MHz -125dBm applied.

2N3055, thanks for doing and posting the measurements.  A couple questions and maybe a request, please, thanks.

1. Why is the amplitude measurement different with the 2kHD vs 3kHD?
2. What happens when you run the modulation test on the 2k?  Similar results but just takes longer to complete?

One is without and other one with modulation. Difference is about 1dB. I'm guessing it's the AWG when modulation got on.. I didn't care because what was important was accurate 6db relation.

On 2k looks pretty much the same and pretty much lasts the same, because at this settings most of the time is acquisitions and averaging not FFT processing time.

5

Repair / Re: Help needed for repair of Efratom FRS-C rubidium oscillator

« Last post by edpalmer42 on Today at 09:09:07 pm »

* The fan only turns on when the counter is taken out of standby. The remarkable thing is that the fan is cooling the
supply of the Rubidium oscillator, which is on all the time. That power supply needs to work just as hard
when the counter is in stand-by as when it is on. So I don't get it... Is it perhaps the case that when the counter is on,
the fan is supposed to create a more stable temperature environment for the oscillator? (By the way,
that would also explain why the fan is allowed to be operated from a different power supply, which may break...)

You should take a close look at the power for the fan.  I think that if the Rb is installed, the fan is supposed to run continuously.  There might be another problem or an option set wrong.  You could remove the Rb oscillator, power supply, and distribution board and put them into a seperate box.  This would allow you to set up a nice passive heatsink with no fan to cool the Rb.

* When the 10 MHz clock is not there, apparently the display remains empty. But the software is very much alive.
So why is there not some error message displayed? Or at least some kind of sign of life? This boggles my mind.

The software isn't alive when the counter is in standby.  What are the power supplies drawing in standby?  The power switch turns the +5V on/off as described in the power supply section of the manual.  The reason the oscillator is necessary is that it acts as the clock for the CPU.  I've also seen that in a counter from Racal.

Anyway, after installing the replacement supplies, it looks like I will be able to see how accurate the counter is,
after I hook up my GPSDO. I will keep you posted on that part as well.

Again, many thanks for the advice and moral support! EJ

You're welcome.  Glad I could help.

Ed

6

Buy/Sell/Wanted / Re: FS (EU/WorldWide) Logic analyser Hantek LA5034

« Last post by xvr on Today at 08:58:06 pm »

Yes, CD was included, but version is very outdated (for now). CD content available, physical CD is not. Unfortunately I can't right now check CD version (I'm on vacation till May 8 and not at computer)

7

Microcontrollers / Re: Memory model for Microcontrollers

« Last post by tellurium on Today at 08:57:33 pm »

When you compile C code for a desktop OS, the reference to startup code and startup entry point is automatically inserted by the compiler.

When you compile the code for desktop, you produce an ELF file. An ELF file has a "entry point" symbol. You can check the entry point by using objdump:

Code: [Select]

$ objdump -f ~/tmp/wizard/firmware.elf
...
start address: 0x30007a39

For the ARM firmware file, the entry point is basically ignored, because firmware binary is produced and flashed as I described earlier. The entry point is used by debuggers - by fetching an entry point from a firmware.elf, a debugger knows where to set a default breakpoint. An entry point is specified by a linker script. It is usually set to a reset handlier, e.g.: https://github.com/STMicroelectronics/cmsis_device_h7/blob/88f29645ec7e063bae3d5e58699fc541a81efac6/Source/Templates/gcc/linker/stm32h747xx_flash_CM7.ld#L35

On a desktop system, the situation is different. As far as I understand, there is a standard, called ABI (application binary interface). It says that on UNIX systems, an entry point of a binary should be a symbol called "_start".  When a unix kernel starts a process, it loads the first page of an executable file into memory, and loops over a list of so called "image activators". Those are functions that recognise file format and try to start an executable. There are image activators for ELF files, for shell scripts, etc etc.

So ELF image activator looks for and ELF signature at the beginning of the file, and if it finds it, it scans the ELF header for the _start symbol. Then it does a bunch of other things, and it jumps to _start. A function _start is part of a C runtime - it is located in a file crt*.o, which gets linked to your binary at the build stage, as Nominal Animal pointed out.  This part of C runtime implements an ABI - that's why it is separate from a C library itself. A function _start loads dynamic libraries, prepares argv, argc, environ, and then calls main().

So when you say "reference to startup code and startup entry point is automatically inserted by the compiler." - yeah, pretty much. By the linker. The startup code is that _start function.

8

Projects, Designs, and Technical Stuff / Re: A naive question about automotive CANbus sniffing and spoofing

« Last post by Smokey on Today at 08:54:56 pm »

...
The Cash for Clunkers program was an attempt to get rid of (buy up and destroy)  as many old cars as possible.
...

To full lean into the off-topicness of this....

I know a guy that ran a two bay automotive repair show here in town.  He said that the "cash for clunkers" program crushed his business, which for a large part was repairing those clunkers.  Collateral damage.

9

Test Equipment / Re: Siglent SDS800X HD Review & Demonstration Thread

« Last post by markone on Today at 08:52:55 pm »

Interesting we see some signal "artifacts" on the Rigol #0 but not on the Siglent #52. Signal is from AWG (SDG2042X) at 2mvpp @ 50 ohms (-50dBm). Both have Flattop Windows, Signal has 4 average (not available on Rigol). BTW these artifacts originate within the Rigol and not from the AWG.

-snip

For what is worth, my DHO1000, same signal :





Here below what my SSA read :

10

Beginners / Re: How Current Limitation is happening in the circuit???

« Last post by MrAl on Today at 08:44:27 pm »

Here are some charts that illustrate the effect of the capacitor value and the total input impedance Rs.



All of these are with an input sine wave peak of 30 volts and two diode drops 1.15 volts each,
frequency was 50Hz, Rload=3 Ohms.

Units: Volts, Ohms, Farads.


C=0.001000
Rs=0.00  Vmax=19.00  Vmin= 6.60  Vpp=12.398
Rs=0.10  Vmax=18.38  Vmin= 6.60  Vpp=11.782
Rs=0.20  Vmax=17.78  Vmin= 6.58  Vpp=11.200
Rs=0.30  Vmax=17.21  Vmin= 6.56  Vpp=10.651
Rs=0.40  Vmax=16.66  Vmin= 6.53  Vpp=10.134
Rs=0.50  Vmax=16.14  Vmin= 6.49  Vpp= 9.648
Rs=0.60  Vmax=15.64  Vmin= 6.45  Vpp= 9.191
Rs=0.70  Vmax=15.17  Vmin= 6.40  Vpp= 8.762
Rs=0.80  Vmax=14.71  Vmin= 6.35  Vpp= 8.358
Rs=0.90  Vmax=14.28  Vmin= 6.30  Vpp= 7.979
Rs=1.00  Vmax=13.87  Vmin= 6.25  Vpp= 7.623

C=0.005000
Rs=0.00  Vmax=27.10  Vmin=17.55  Vpp= 9.550
Rs=0.10  Vmax=25.92  Vmin=17.37  Vpp= 8.560
Rs=0.20  Vmax=24.37  Vmin=16.88  Vpp= 7.489
Rs=0.30  Vmax=22.64  Vmin=16.19  Vpp= 6.454
Rs=0.40  Vmax=20.91  Vmin=15.39  Vpp= 5.521
Rs=0.50  Vmax=19.27  Vmin=14.55  Vpp= 4.714
Rs=0.60  Vmax=17.76  Vmin=13.72  Vpp= 4.034
Rs=0.70  Vmax=16.40  Vmin=12.93  Vpp= 3.467
Rs=0.80  Vmax=15.19  Vmin=12.19  Vpp= 2.997
Rs=0.90  Vmax=14.11  Vmin=11.50  Vpp= 2.607
Rs=1.00  Vmax=13.15  Vmin=10.87  Vpp= 2.282

C=0.010000
Rs=0.00  Vmax=27.55  Vmin=21.46  Vpp= 6.082
Rs=0.10  Vmax=25.50  Vmin=20.61  Vpp= 4.896
Rs=0.20  Vmax=22.25  Vmin=18.64  Vpp= 3.614
Rs=0.30  Vmax=19.02  Vmin=16.41  Vpp= 2.609
Rs=0.40  Vmax=16.28  Vmin=14.37  Vpp= 1.906
Rs=0.50  Vmax=14.08  Vmin=12.65  Vpp= 1.427
Rs=0.60  Vmax=12.33  Vmin=11.23  Vpp= 1.097
Rs=0.70  Vmax=10.92  Vmin=10.06  Vpp= 0.865
Rs=0.80  Vmax= 9.79  Vmin= 9.09  Vpp= 0.696
Rs=0.90  Vmax= 8.85  Vmin= 8.28  Vpp= 0.571
Rs=1.00  Vmax= 8.07  Vmin= 7.59  Vpp= 0.476

C=0.015000
Rs=0.00  Vmax=27.63  Vmin=23.17  Vpp= 4.464
Rs=0.10  Vmax=24.33  Vmin=21.20  Vpp= 3.126
Rs=0.20  Vmax=19.41  Vmin=17.51  Vpp= 1.906
Rs=0.30  Vmax=15.43  Vmin=14.24  Vpp= 1.186
Rs=0.40  Vmax=12.56  Vmin=11.78  Vpp= 0.783
Rs=0.50  Vmax=10.51  Vmin= 9.96  Vpp= 0.548
Rs=0.60  Vmax= 9.00  Vmin= 8.59  Vpp= 0.402
Rs=0.70  Vmax= 7.85  Vmin= 7.54  Vpp= 0.306
Rs=0.80  Vmax= 6.95  Vmin= 6.71  Vpp= 0.241
Rs=0.90  Vmax= 6.23  Vmin= 6.04  Vpp= 0.194
Rs=1.00  Vmax= 5.64  Vmin= 5.48  Vpp= 0.159

C=0.020000
Rs=0.00  Vmax=27.66  Vmin=24.13  Vpp= 3.532
Rs=0.10  Vmax=22.87  Vmin=20.77  Vpp= 2.104
Rs=0.20  Vmax=16.78  Vmin=15.70  Vpp= 1.080
Rs=0.30  Vmax=12.67  Vmin=12.07  Vpp= 0.608
Rs=0.40  Vmax=10.03  Vmin= 9.65  Vpp= 0.379
Rs=0.50  Vmax= 8.25  Vmin= 8.00  Vpp= 0.257
Rs=0.60  Vmax= 6.99  Vmin= 6.81  Vpp= 0.184
Rs=0.70  Vmax= 6.06  Vmin= 5.92  Vpp= 0.138
Rs=0.80  Vmax= 5.34  Vmin= 5.23  Vpp= 0.108
Rs=0.90  Vmax= 4.77  Vmin= 4.68  Vpp= 0.086
Rs=1.00  Vmax= 4.31  Vmin= 4.24  Vpp= 0.070

C=0.025000
Rs=0.00  Vmax=27.68  Vmin=24.75  Vpp= 2.926
Rs=0.10  Vmax=21.32  Vmin=19.86  Vpp= 1.465
Rs=0.20  Vmax=14.58  Vmin=13.92  Vpp= 0.653
Rs=0.30  Vmax=10.64  Vmin=10.30  Vpp= 0.345
Rs=0.40  Vmax= 8.29  Vmin= 8.08  Vpp= 0.208
Rs=0.50  Vmax= 6.76  Vmin= 6.62  Vpp= 0.138
Rs=0.60  Vmax= 5.69  Vmin= 5.59  Vpp= 0.098
Rs=0.70  Vmax= 4.91  Vmin= 4.84  Vpp= 0.073
Rs=0.80  Vmax= 4.32  Vmin= 4.26  Vpp= 0.057
Rs=0.90  Vmax= 3.85  Vmin= 3.81  Vpp= 0.045
Rs=1.00  Vmax= 3.47  Vmin= 3.44  Vpp= 0.037

C=0.030000
Rs=0.00  Vmax=27.68  Vmin=25.18  Vpp= 2.500
Rs=0.10  Vmax=19.79  Vmin=18.74  Vpp= 1.049
Rs=0.20  Vmax=12.78  Vmin=12.36  Vpp= 0.419
Rs=0.30  Vmax= 9.12  Vmin= 8.91  Vpp= 0.212
Rs=0.40  Vmax= 7.03  Vmin= 6.91  Vpp= 0.125
Rs=0.50  Vmax= 5.70  Vmin= 5.62  Vpp= 0.082
Rs=0.60  Vmax= 4.79  Vmin= 4.73  Vpp= 0.058
Rs=0.70  Vmax= 4.12  Vmin= 4.08  Vpp= 0.043
Rs=0.80  Vmax= 3.62  Vmin= 3.59  Vpp= 0.033
Rs=0.90  Vmax= 3.23  Vmin= 3.20  Vpp= 0.026
Rs=1.00  Vmax= 2.91  Vmin= 2.89  Vpp= 0.021

C=0.050000
Rs=0.00  Vmax=27.69  Vmin=26.11  Vpp= 1.586
Rs=0.10  Vmax=14.73  Vmin=14.39  Vpp= 0.342
Rs=0.20  Vmax= 8.35  Vmin= 8.24  Vpp= 0.107
Rs=0.30  Vmax= 5.72  Vmin= 5.67  Vpp= 0.050
Rs=0.40  Vmax= 4.34  Vmin= 4.31  Vpp= 0.029
Rs=0.50  Vmax= 3.49  Vmin= 3.47  Vpp= 0.019
Rs=0.60  Vmax= 2.91  Vmin= 2.90  Vpp= 0.013
Rs=0.70  Vmax= 2.50  Vmin= 2.49  Vpp= 0.010
Rs=0.80  Vmax= 2.19  Vmin= 2.19  Vpp= 0.007
Rs=0.90  Vmax= 1.95  Vmin= 1.94  Vpp= 0.006
Rs=1.00  Vmax= 1.76  Vmin= 1.75  Vpp= 0.005

C=0.075000
Rs=0.00  Vmax=27.70  Vmin=26.60  Vpp= 1.093
Rs=0.10  Vmax=10.77  Vmin=10.65  Vpp= 0.120
Rs=0.20  Vmax= 5.73  Vmin= 5.70  Vpp= 0.034
Rs=0.30  Vmax= 3.87  Vmin= 3.86  Vpp= 0.015
Rs=0.40  Vmax= 2.92  Vmin= 2.91  Vpp= 0.009
Rs=0.50  Vmax= 2.34  Vmin= 2.33  Vpp= 0.006
Rs=0.60  Vmax= 1.95  Vmin= 1.95  Vpp= 0.004
Rs=0.70  Vmax= 1.67  Vmin= 1.67  Vpp= 0.003
Rs=0.80  Vmax= 1.47  Vmin= 1.46  Vpp= 0.002
Rs=0.90  Vmax= 1.30  Vmin= 1.30  Vpp= 0.002
Rs=1.00  Vmax= 1.17  Vmin= 1.17  Vpp= 0.001

C=0.100000
Rs=0.00  Vmax=27.70  Vmin=26.86  Vpp= 0.835
Rs=0.10  Vmax= 8.38  Vmin= 8.32  Vpp= 0.054
Rs=0.20  Vmax= 4.35  Vmin= 4.33  Vpp= 0.014
Rs=0.30  Vmax= 2.92  Vmin= 2.91  Vpp= 0.007
Rs=0.40  Vmax= 2.20  Vmin= 2.19  Vpp= 0.004
Rs=0.50  Vmax= 1.76  Vmin= 1.76  Vpp= 0.002
Rs=0.60  Vmax= 1.47  Vmin= 1.46  Vpp= 0.002
Rs=0.70  Vmax= 1.26  Vmin= 1.26  Vpp= 0.001
Rs=0.80  Vmax= 1.10  Vmin= 1.10  Vpp= 0.001
Rs=0.90  Vmax= 0.98  Vmin= 0.98  Vpp= 0.001
Rs=1.00  Vmax= 0.88  Vmin= 0.88  Vpp= 0.001