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Have you checked that the output of the first stage is near 0V. The input bias currents of the AD797 are too high to use 20M for the biasing, try 1M, same as the feeback resistor - for now.
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Test Equipment / Re: EEVblog 121GW Multimeter Issues
« Last post by Scottjd on Today at 09:07:15 pm »
My meter arrived a couple of days ago followed by an email from Kick-starter telling me it was my last chance to update my shipping details :)

Mine arrived with an immediate problem.  The screen contrast and viewing angles were weird and touching the screen even very lightly caused various segments to come on.  The packaging was largely OK, some bumps and bruises.

Anyway I gave the meter a bump on my bench (just on the top edge of the rubber surround) front and back.  Problem solved.  Not sure if the screen suffered a squish in transit or if it was pushed to hard front or back during assembly but I am thinking it was one or the other.  If you have this problem you can try giving the thing a bump.  Worked for me but, as they say, YMMV.
Mine has a weird viewing angle also, straight on is dim compared to looking up at it. But looking at a down angle it get worse, almost unreadable.

If you hold the RANGE button down when you turn it on, it will display all the LCD characters so you can check the LCD or see if some of the zebra connections are not making good contact.
Scott
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-GSM module.
Ring once toturn on, ring twice to turn off.
Or send SMS.
-Wifi module.
Add very directional antenna for extended range.
-Powerline ethernet module.
-LoRa module.
-'Hacked' RF device thathas sufficient range.
For example some walkietalkie or FM bug.
Then transmit a short tone to turn on or off.
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Test Equipment / Re: EEVblog 121GW Multimeter Issues
« Last post by Scottjd on Today at 09:03:33 pm »
I have one more for you I forgot about, but also probably related to the hold code.
In Amp if you measure current, hold the reading and pull the probes out the reading stays displayed.
In the mA/uA jack if you do the same thing when you pull the probe out, the screen goes blank. And if you had it set to a manual range it changes over to Auto range when you pull the probe with the reading on hold.
Some flukes do this from the jack detection warning, but when you put the probe back in the measurement is displayed again on the LCD. When I plugged it back in the mA/uA jack I was hoping it would display again but it didn’t. Then I realized it’s becjase it reset to Auto ranging also.
Scott
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Thermal Imaging / Re: Flir One compatibility with Axon 7
« Last post by TheNetStriker on Today at 09:01:37 pm »
The FLIR One and One Pro are not worth your money.
Buy a Seek Compact Pro for the same money and get 4 times the resolution.

Thanks for the hint. I just saw that the device has an micro usb connector. Can this device be attached to USB-C using an adapter? And how can I be sure that the device will be compatible with my phone?
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Test Equipment / Re: waveform generator advice
« Last post by Performa01 on Today at 08:59:19 pm »
Always some good recommendations on here!

I'm also looking for an arbitrary waveform generator with sweep functions in the audio range (10Hz-100KHz).

However, I don't need low distortion or noise, necessarily.  I have a modified Heathkit IG5218 which I'll actually be using for a measurement signal source - but I need something to provide a swept signal, tone burst, etc. in order to get a quick visual indication of how the signal is being changed by the device under test.  It would be nice if the generator had a stable output level and accurate frequency, but I sure don't need a lot of bells and whistles.

I know I could use a laptop and the audio output, but there are some hassles with that:

1) I only use Macs, and software is harder to locate (I'm not buying yet another computer!)
2) Setting up the computer for a quick measurement (which often involves retrieving it from elsewhere in the house) takes longer than the measurement
3) I need flat frequency response up to about 100KHz and I'm sure that's harder to do on a computer

Thoughts?


For your application, the combination of the SDS1104X-E DSO and SAG1021 AWG option might be worth considering.

The AWG has a THD well below 0.1% up to 2MHz and together with the scope can provide a nice (up to) 3-channel bode plot without a computer. Yet the scope can be remote controlled from a PC with any OS via its webserver and you even get a pretty fast real time display with the latest firmware.

A (still incomplete) review can be found here:
http://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/50/

The review of the SAG1021 is in replies #48 and #49 and a brief demonstration of the bode plotter can be found in reply #67
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Microcontrollers & FPGAs / Re: Cortex M7 and DMA
« Last post by Siwastaja on Today at 08:56:17 pm »
Can anyone suggest where to find good information or tutorial on DMA for STM32

The reference manual. In STM32, the DMA is fairly straightforward and just works; quite sure it's very similar on most ARM MCUs. Not too many registers to configure; set the source and destination addresses, data sizes, num of transfers, and the DMA request channel numbers, and off you go. There are some small catches like the need to clear interrupt flags before enabling the DMA on STM32, but it's still about 5-10 lines of code total to make it work.

If it takes more than 30 minutes, or more than 10 lines of code, with any library/framework/whatever, the library fails its only job (making things easier to use than without it), and can be simply ditched.

For me, it's hard to believe the lack of information you describe. DMAs should be documented in the reference manuals for any ARM MCU vendor; maybe some Chinese ultra cheap or otherwise "weird" processors might be an exception.

The most difficult aspect is working around DMA request matrix connectivity limitations (depending on MCU, of course; I had quite hard time on STM32F205 recently). If you only need DMA for one peripheral only, everything's simple, but if you need multiple (simultaneously), you need to extend your PCB design time considerations so that you not only look which peripheral is available at which pins, but also whether these peripherals can all work on DMA simultaneously, to avoid ugly surprises when your design is already built and you are developing the software. For example, USART1 and SPI1 might not be available through DMA simultaneously, but USART2 and SPI1 would work; this needs to be thought over during schematic and layout capture.
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General Chat / Re: What to listen to over RTL-SDR?
« Last post by RoGeorge on Today at 08:54:50 pm »
Not exactly listening, but receiving images from weather satellites
https://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-noaa-weather-satellite-images/
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Metrology / Re: Valhalla 2701C (kinda working!?)
« Last post by LainisLain on Today at 08:54:20 pm »
Update!

In answer to your questions. Yes the terminals appear to be connected correctly. Yes I've checked most of the diodes. And yes I may have found a bad HV transistor!

TR7-11 are a mix of FQP3N90 and SSP2N90. Possibly some have been replaced at some point. I was probing around with my DMM in diode mode and saw that TR10 was conducting from gate to source in both directions! I removed (what a pain in the a$$!) and sure enough my part tester shows double diode!

https://drive.google.com/open?id=12_0FITgLfs8mv6nClZFAnrR9qFvCWycs
https://drive.google.com/open?id=1qe_wSBEApUGylwa3WPTy2g9yuhiMPNww


At this point i'm just going to replace all the HV transistors and recap all the HV caps. I was looking at FQP4N90C for a replacement. Can anyone see an issue with that?

Thanks again and I'll keep you updated.  8) 
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Maybe putting an line driver ic in the lcd line ??? are you sure it has standard 14 or 16 pins (lcd) pinout  ??

Why 12vdc on the RAW pin ??   doesnt seems right to me ??  second schematic
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