kimmoli | # 1 | 2014-04-09, 07:04 | Report

Multimeter

Icon by solbrit

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Last edited by kimmoli; 2014-04-09 at 08:45.

kimmoli | # 2 | 2014-04-09, 07:09 | Report

New TOH idea by bill_klpd, Multimeter TOH.

Seems that i started to think about this further.

First, sketching the UI:


Block diagram of the electronics part: (First draft)


First 3D sketch:


HW Specs:

• Voltage measurement ranges 200mV, 2V, 20V, 200V DC (AC TBD)
• Current measurement 200mA, 2A (TBD)
• Resistance measurement 200, 2k, 200k, 20MEGohms (TBD)
• Possibility to measure low-side current and high-side voltage at the same time --> Power (W) measurement.
• Isolated from phone (floating) should be safe to keep USB charger connected while taking measurements.
• Fused current measurement

SW Specs:

• Continuous measurements with adjustable rate
• Min/avg/max display
• Single shot measurement when in hold mode
• Beep when new min max value, or beep when short in Resistance mode.
• Logging of readings with timestamps
• Trigger events with alerts also possible TBD
• "Plotter" view on separate page of latest results TBD
• or simpler graph view in main page TBD

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Last edited by kimmoli; 2014-04-11 at 07:51.

coderus | # 3 | 2014-04-09, 07:11 | Report

future is coming!

also please add short circuit mode checking with beep signal.

juiceme | # 4 | 2014-04-09, 07:30 | Report

Hmmh, why not an oscilloscope, or at least a possibility to plot voltage changes over time...

Usually multimeter functionality is implemented by sampling the voltage in analog hold, and then measuring the time differential when bleeding it off through a known resistance. (this allows for really accurate measurement with no A/D converter needed, and is easy/cheap to implement with a dedicated chip).

However with a real fast-sampling A/D conversion it woud be possible to get the waveform plot too.

coderus | # 5 | 2014-04-09, 07:54 | Report

why not? i'm just asking what i want

juiceme | # 6 | 2014-04-09, 08:12 | Report

Sorry, I meant to add a post, not reply to yours!
Continuity beep is a good feature, yes.

However, what I'd like to have is the scope mode

kimmoli | # 7 | 2014-04-09, 08:12 | Report

See specs ^^
Note; This is not a oscilloscope. That toh will be done later with its own micro to buffer/preprocess samples.

For me that is also an A/D converter

However with a real fast-sampling A/D conversion it woud be possible to get the waveform plot too.[/QUOTE]
Maximum samplerate with A/D converter selected (atm) is 860 sps.

400kHz I2C limits samplerate to about 7ksps, (at 16bits) but when taking IOCTL etc into account, maybe something like 10 sps in realtime could be doable without buffering...
(if taking samples in background for a short period of time, 860sps is doable)

nieldk | # 8 | 2014-04-09, 08:23 | Report

I would really like to see a logic analyzer

kimmoli | # 9 | 2014-04-09, 08:44 | Report

Logic analyzer will be in tohscope

bill_klpd | # 10 | 2014-04-09, 08:58 | Report

Great work kimmoli! Keep up