Hi
I am using my K8055 USB experiment board to measure and log the driving voltage of circuit. I am using a voltage regulated bench power supply and my bench multimeter confirms a steady 4.61V. However the velleman board is displaying continually varying voltage of 4.65-4.76 V at its analogue input. Can the stability of the measured voltage via the analogue input be improved upon?
Note that multimeters usually do some averaging, so you won’t see any noise with them. If you really want to know what is going on you will have to use an oscilloscope.
The problem you describe is often caused by noisy USB supply voltage, either from the computer itself or caused by low quality USB cables with bad shielding and noise from induction. The K8055 uses the +5V USB power as reference voltage for ADC.
Try using different cables, different ports or a powered USB hub with a stable and low noise supply voltage. I have built myself a powered mini-hub by adding a power connector, a UA7805 voltage regulator and a few capacitors to a small notebook USB hub:
That way the reference voltage is stable enough to use even 10-bit ADC on the K8055 (obviously with a different PIC).
Regards,
Jan
Thanks
Makes sense.
Oscilloscope shows about 40mV peak to peak noise on the monitored circuit. Do you by any chance have a circuit diagram for your powered USB hub?