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Velleman HPS140 Pocket Oscilloscope

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Front of PCB. Processor is dsPIC33FJ64GP204. Above is TI TPS76633 3.3v regulator, with a second one at the right, presumably a seperate regulator for the analogue front-end.

One minor mod on the PCB - this is probably the first production run.Transistor at right is part of a rather crude constant-current charge circuit.

A notable absence is a crystal, however a simple instrument like this isn't going to be used for accurate frequency measurements so not really a big deal. The PIC's on-chip RC oscillator is specced to +/-2%. The spec doesn't even quote a figure for timebase accuracy!

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Rear - mostly occupied by battery and front-end circuitry under the shieling can. Note ISP header top-left.     The big round pad top centre is a probe cal signal, accessable through a hole in the rear of the case.

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Inside the can. Mostly taken up by four reed relays. LMV934 quad opamp top centre, NXP ADC0801S040 ADC top right . OPA2354 high-speed amp at centre right is the main gain stage. A few twiddles for calibration. Holding the menu button down on powerup appears to put it into a calibration mode.


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Current draw is 105-130mA depending on range and AC/DC selection (i.e which relays are on).
Backlight starts dropping out at 4.2V. scope freaks out around 3.6V - there appears to be no form of battery indication or charge management.

Lack of battery level indication is a bit disappointing, as the PIC has an ADC that could do it for minimal cost, however with the 800mAh nominal battery capacity, it should run for a decent amount of time. Nominal charge current is around 140mA, but not particularly well regulated and varies a bit with supply.

This is the USB power lead that comes with it - outputs 9V at 200mA.

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