ul-gh
commented
4 years ago Hi,
please excuse the late reply, I had some busy weeks.
I just now tested with my Raspi and I can not confirm the zeros. However, there is a small issue with your example, please see the comments I made to your file right at the code block at the bottom of this reply.
I do not currently own an RPi 4 - I tested with Raspi 2 and 3 versions. Of course there could be some issue with the Pi 4 which I do not know of yet.
Can you please test if the changes I explaned below fix your issue and if not, can you maybe test with an RPi 3?
Apart from this, maybe I am ordering a Pi 4 in the near future, then I can test the board with the newer hardware.
The issue I found was that you are calling ADS1256.reset() in every loop. This resets the hardware configuration registers and thus these must be re-initialised to the desired values - except you want the hardware defaults (wich is especially with a deactivated input buffer).
Please test this:
#!/usr/bin/python
# -*- coding: utf-8 -*-
""" Based on PiPyADC: Example file for class ADS1256 in module
see https://github.com/ul-gh/PiPyADC
Hardware: Waveshare ADS1256 board interfaced to the Raspberry Pi 3
"""
from __future__ import print_function
import sys
import time
from ADS1256_definitions import *
from pipyadc import ADS1256
import bench_config as conf
# Input pin for the potentiometer on the Waveshare Precision ADC board:
POTI = POS_AIN0|NEG_AINCOM
ads = ADS1256(conf)
# reset() is automatically called during initialisation from the constructor,
# however, if it is explicitly called like this:
ads.reset()
# then by resetting the ADC to base state, it must be re-configured afterwards,
# e.g. activate the input buffer, set data rate etc.
ads.adcon = conf.adcon
ads.drate = conf.drate
ads.gpio = conf.gpio
# This one is important, as it activates/deactivates the input buffer
ads.status = conf.status
def do_measurement():
# You should not call ads.reset() in the loop!
##ads.reset() - NO!
# You /could/ always start the self-calibration routine, however this should
# normally only seldom be necessary, e.g. when temperature changes much.
ads.cal_self()
# The rest is OK
raw_channel_pair = ads.read_oneshot(POTI)
volts = ads.v_per_digit * raw_channel_pair
return volts
while True:
volts = do_measurement()
while volts <= 0:
volts= do_measurement()
print('Measured <= ZERO!')
print('VOLTAGE=', volts)
time.sleep(0.1)
acatphd
First, let me say THANK YOU for developing PiPyADC!! Setup was straightforward and worked "out of the box". I have set it up with the WaveShare High-Precision AD/DA Board on a new RPi4 running Raspian Buster.
I am using the board to measure the drain characteristics of batteries. Simply put , the circuit consists of a load resistor across a battery, the voltage measured across the resistor from AD0 to AINCOM/Ground, using a one shot measurement (I'll attach the code below as a txt file for a simpler portion of the measuring part of the program). The battery voltage is always between 0-1.5 Volts.
The problem is that the reading from either a "one-shot" or "sequence" reading will produce a value of 0 volts in an irregular pattern over time, or, yet more infrequently an erroneous voltage value altogether. I should point out that even running the example code, example.py or example_2.py results in the same behavior. So perhaps my board has some defect. I have noticed that it seems to vary depending on the sample rate and delay values but I'm not sure if this is reproducible. I've checked all my connections etc., but I am wondering if there is some specific settings or code that is critical to reproducible behavior?
Measure.txt