Recent Posts

1

Beginners / Re: The old "Replace blue LEDs with red LEDs" 7 segment question (74HC595)

« Last post by pcprogrammer on Today at 08:48:36 am »

If possible change the 220 Ohm current limiting resistors to 470 Ohm when replacing the 7 segment displays. This will limit the current to about 6mA instead of 13mA the 220 Ohm allows. The 13mA won't kill the red ones but they might be to bright with it and it can kill the 74HC595A because with all segments lit the current will be above the max Icc of 75mA given in the datasheet.

Simple rule is to take the LED forward voltage and subtract it from the supply voltage and divide that by the current limiting resistor to get the operational current. So with a Vf of 3.8V and a supply of 5V and a 220 Ohm resistor it is 5 - 3.8 = 1.2 / 220 = 0,005454 Ampere. Will be a bit less due to the output voltage of the 74HC595A not being equal to the supply voltage.

The 74HC595A has an output enable. Controlling this with a PWM signal can dim the display. The outputs will only supply current when enabled and on average lower the current through the LED thus dimming it.

2

Projects, Designs, and Technical Stuff / Re: Software/Spreadsheet for transformer calculation

« Last post by arjen on Today at 08:47:26 am »

Have you considered creating a database to store and manage transformer data?

3

Repair / Re: Tek FG502 fails at high frequency end of dial - help needed!

« Last post by gcwills on Today at 08:47:03 am »

Thanks very much for taking the time to respond and for your suggestions.
I did try reseating the opamps and also replacing them all to no effect.
I did check the resistors associated with the multiplier and they were all spot on apart from R150 and R186 which read a little over 4M. Replaced them with 3.9M 1% resistors with no effect.
And yes, the signal dropout can be seen at the gate of Q200 so the problem occurs in the circuit before Q200.
I did replace U140 and U175 and tested Q140 and Q175 - all good.
I did find that the associated carbon comp resistors R140 and R175 were reading around 575 ohm - higher than their value of 510 ohm and were replaced with 510 1% metal film - no difference!
I did check all of the timing caps and thought I had a leaky C154 but it turned out to be fine. The caps were tested for value and for leakage with a very sensitive leakage tester - all good.
So the hunt for the elusive issue continues!

4

Test Equipment / Re: Siglent SDM3045X Boot Hang

« Last post by somen on Today at 08:46:43 am »

I had the same issue with my SDM3045X, however I somehow got out of the bootloop by doing the following:
1. Switch off the power supply (or unplug the power cable)
2. Press the on/off button and keep it pressed while switching on the power supply

After this it would boot up and I could install the latest firmware.

I did the manipulations from this post. Unfortunately it didn't help me

5

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by tggzzz on Today at 08:43:15 am »

If you are highly technical person and dont develop your own tool like app in PC, siglent is more polished. And 2GSps is really something, its should be possible to look at near 1GHz RF, such as 433 or 800MHz china RF module digital ASK modulation, something 1GSps scope is incapable, even if frontend BW is hackable. But then which type of guy are you? 

I would hope they are they type of guy that would use an appropriate tool.

• for many RF measurements that means a frequency-domain or modulation-domain instrument (a scope is time-domain)
• for amplitude shift keying (ASK), that means an "RF probe"

With one of those they could use any scope with a bandwidth that exceeds the signal bandwidth/baudrate (which has nothing to do with the RF carrier frequency).

Example RF probe: hp11096a/b. While that's only characterised to 700MHz, with modern components it would be trivial for an amateur to build a higher frequency equivalent.

6

Test Equipment / Re: Siglent SDS3000X HD and upgraded SDS1000X HD

« Last post by ebastler on Today at 08:40:42 am »

Up to 5-7,000 euros are not really unaffordable for a more powerful amateur or a very small company.
So an SDS3000X HD would be just the thing.

Not everyone can have easy access to a demo unit.
A review and a teardown might convince. Not to mention the excellent tests you did for some models.

But what kind of review do you expect Dave to do? In preparing a video, he cannot spend days and weeks to really dig into the subtleties of a device as powerful and complex as the 3000X HD. And his video format does not allow for the level of detail which Performa01 presented in his 800X HD thread -- nowhere near, in fact.

Let's face it: The EEVblog videos are about entertainment, not about the in-depth assessment one would want to do before spending 5000€ and more. For professional customers, getting a demo unit would probably be the way to go. And for serious amateurs, at least in Europe, you can always buy a unit, test it for 2-4 weeks, and return it in case of major disappointments.

7

Repair / DMM6500 Keithley Error Code 1153

« Last post by faster91 on Today at 08:39:21 am »

I have a Keithley DMM6500 6.5 Digit Multimeter. Few days ago I encountered in the error 1153.
The Error Code 1153 indicates a problem with the internal power supply. I tried to update the firmware and checked the voltage at the source, but it was ok.

Does anyone have any suggestion?

Thanks.

8

Microcontrollers / SD Card reliability in SPI mode

« Last post by betocool on Today at 08:39:01 am »

Hey all,

more a general question than looking for a specific answer, but would like to know your experiences in this matter.

I'm using an NRF52840 (u-blox) connected to an SD Card using the SPI interface. Filesystem is FatFS as far as I can tell. Basically the file system and the SD interface are all set up automagically by Zephyr. Good or bad, no point arguing that, but comfortable.

This device writes at low speeds, 10 KBytes per second at most (so far) from a buffer, always trying to write out multiple of 512 bytes at a time. It's not too busy. After each write, I call the flush() or sync() function (don't have the code in front of me) to make sure the data persists on the SD card.

Data files can be displayed and then be retrieved over bluetooth, and that also works a treat, reading at about 500 kbps.

So far, so good.

In time, after much use (days? weeks?) the SD cards I've used seem to deteriorate. I can read them on Windows, it doesn't complain, but the micro either fails to init them, or sometimes it does init them but it can't read the file listing. Yet, if it inits them it seems to write data. Sometimes it can't do anything.

Swap the SD card and everything seems to work well again for a few days / weeks.

I still need to improve on a few things. When the micro is reset, the power to the SD card is off (no 3.3v), when a BLE connection is detected, the power to the 3.3V is turned on, card init'd and ideally all works. If I don't reset the unit explicitly, the 3.3V to the SD card would stay on indefinitely. That is something I need to fix. If not doing it's data logging, the unit just stays on basically. I'm sure I've covered most cases, it's unlikely that files are not closed after the micro's work is finished. Then again, I confess I have not tested all possible issues.

I wonder if you guys have experienced similar issues with SD cards using SPI? If so, if you were able to fix them or improve the reliability, what did you do?

Cheers,

Alberto

9

Test Equipment / Re: Siglent SDM3045X Boot Hang

« Last post by somen on Today at 08:37:12 am »

I bought the SDM3045X at the end of December 2022. Yesterday, when I turned it on, I encountered a similar problem - the logo is displayed on a black background and that’s it. The warranty was one year.
Dear tautech, сan you send me the recovery tool please?

10

Other Equipment & Products / Re: Pace ADS200 soldering station

« Last post by SteveyG on Today at 08:29:59 am »

When I can get hold of it in the UK, I'll test out the new version.
Don't worry I have no bias here, but I never really got to the bottom of my issues with the original ADS200. It simply doesn't deliver - I've tried to use it extensively but it always fails on anything other than light duty work, so I'm not sure if mine was faulty.