Velleman HPS140 Pocket Oscilloscope
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
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.
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.
Current draw is 105-130mA depending on range and AC/DC selection (i.e which relays are
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.