Electronics > Projects, Designs, and Technical Stuff
Community Bench Meter
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SockThief:
It feels a bit like a kitchen in a cooking school at the moment, with everyone throwing in their own wishes, stirring it about, its going to be interesting to see what comes out. This is the part I always like about community based open-source projects, it can be anything at all! It's like giving a list to Santa and getting it all! (and yes there are probably a few people reading this at the moment, that feel a little underwhelmed by the iPad unveiling last night. The actuality had no hope of living up to the expectactions, we have no such limitations!) But this brings to me a small idea that has been floating around for a while, I always have my iPhone with me. And currently there are iPhone bases Oscilloscopes, meters etc. But as far as I can recall (I actually haven't looked at them for a while) they use the internal H/W to perform A/D conversion etc. So there are strong limitations there.

But! What if there was an external module that communicated by Wi-Fi to the iPhone (or any other smart phone or Wi-Fi equipment for that matter) but let's assume an iPhone, passed all the measurements to the iPhone, then the iPhone could postprocess the results for display, emailing, sms etc. There is no reason why a PC could not stand in for this function, or another custom build module. In any case, by using an iPhone you have
- data which is as high-a-quality as possible (after all its coming from a purpose designed piece of equipment)
- a display is already available
- a ready made communication chanel between the data-collector and the display
- a ready made data analyser
- 3G on the phone allows you to phone-home data to HQ (perfect for in the field work)

just another idea to throw into the pot. I guess this is something Im more than willing to look into and play around with. And can largely be done in isolation from the rest of the project, merely relying on a communications protocol.

Til next time!
xani:
Well, if u have ethernet u can connect it to pretty much everything everywhere :)
Another idea:
Maybe split it into 2 parts, analog input + simple uC to interact with A/D Conv. + "head" with screen and all other measurement functions connected by infrared or optocoupler. So when something fails on analog part, digital part with SD/USB/Ethernet and other fancy stuff is safe. Would be easier than isolating USB
jahonen:

--- Quote from: xani on January 28, 2010, 09:47:43 pm ---Well, if u have ethernet u can connect it to pretty much everything everywhere :)
Another idea:
Maybe split it into 2 parts, analog input + simple uC to interact with A/D Conv. + "head" with screen and all other measurement functions connected by infrared or optocoupler. So when something fails on analog part, digital part with SD/USB/Ethernet and other fancy stuff is safe. Would be easier than isolating USB

--- End quote ---

Agilent power supplies controllable via GPIB or Ethernet are done just this way. Probably their bench DMMs too. One should be very careful about the isolation. Handheld DMM is especially critical since it is "hand held". Bench thing is somewhat easier in that sense.

Ethernet line transformers are tested 1 kV RMS isolation, but that is not enough for safety. Something like 5000 V RMS would be more appropriate there. But anyway without extensive testing, there is no way to guarantee safety (or any CAT-rating), as Mr. Maxwell tends to be more imaginative than we poor design engineers ;)

Add capacitor ESR measurement to the functionality list. This should work downto 1 milliohm (4-wire measurement required?), since most ordinary electrolytics are rated something like 10-20 milliohms.

Regards,
Janne
GeekGirl:

--- Quote from: jahonen on January 29, 2010, 10:08:32 am ---
--- Quote from: xani on January 28, 2010, 09:47:43 pm ---Well, if u have ethernet u can connect it to pretty much everything everywhere :)
Another idea:
Maybe split it into 2 parts, analog input + simple uC to interact with A/D Conv. + "head" with screen and all other measurement functions connected by infrared or optocoupler. So when something fails on analog part, digital part with SD/USB/Ethernet and other fancy stuff is safe. Would be easier than isolating USB

--- End quote ---

Agilent power supplies controllable via GPIB or Ethernet are done just this way. Probably their bench DMMs too. One should be very careful about the isolation. Handheld DMM is especially critical since it is "hand held". Bench thing is somewhat easier in that sense.

Ethernet line transformers are tested 1 kV RMS isolation, but that is not enough for safety. Something like 5000 V RMS would be more appropriate there. But anyway without extensive testing, there is no way to guarantee safety (or any CAT-rating), as Mr. Maxwell tends to be more imaginative than we poor design engineers ;)

Add capacitor ESR measurement to the functionality list. This should work downto 1 milliohm (4-wire measurement required?), since most ordinary electrolytics are rated something like 10-20 milliohms.

Regards,
Janne

--- End quote ---


Hi Janne, I would like to add ESR, should not be too hard :)

I have isolation for my Tek TDS220, I use an isolation box I built as a project for my networks course I did back in '98. It is about 4m of optic fibre cable and TX / RX pairs, it isolates RS232 (in each direction Max232 - Tx Led - Fibre Cable - Rx photo diode - Max232. Both ends were powered by 9v batteries, an would run for about 16 hours)

That could be an option for this project. I am yet to find any decent voltage rated isolation devices (ie >10Kv)
Mastro Gippo:
Yes, ESR and Dave's uCurrent are a must!  ;)
I'm a bit scared of ARMs, that's why I was supporting PICs.. But if someone manages to get an easy bootloader working, I can try to join the fun! I've been thinking about learning ARMs for a while... Maybe we can start on the mBed platform, http://mbed.org/! All the hard part is already done.
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