Its a Velleman HPS10 scope.
V= -.1
Vmax = 1.1
Vmin = -.037
the probe is set to x1
Does this mean the amplitude is max + abs(min-): 1.47
I said 0.4V from the readings off my other mutimeter as it pulsed between .4V and .5V I assumed it was reading the average, I’m taking just off the PWM and GND signals. I’m taking GND off the return in the battery compartment, is this wrong?
Can I put a .bmp on this forum, perhaps I can post a picture to show where I’m going wrong.
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The result is still quite low. Maybe it is anyhow correct measuring result you got.
You may check the result by using the vertical markers (cursors) on the screen to measure the amplitude of the signal.
See page 16 of the manual.
Click the ”mark 1-2” button and use up and down arrows to adjust the other horizontal line at the top of the waveform. Click again the ”mark 1-2” button and use up and down arrows to adjust the second horizontal line at the bottom of the waveform.
You’ll see the amplitude of the signal on the right side of the display (ref 3 on page 16 of the manual).
The multimeter result also indicates that the peak value is about 1V. If the duty cycle of the signal is about 50% then the multimeter displays half of the peak value.
About posting the bitmap images:
See the FAQ: forum.velleman.be/faq.php
Can I post Images?
Some progress
I;m sorry, I had taken the GND off the wrong connection. There are 2x3V litium in the battery box and I too k the wrong pin. Now I have:
116Hz from pulse to pulse
amplitude 2.8V
10K resistor / 4.7µF
I get a rapid signal on AD1 measuring between 80 and 125 and all the values between.
Is it just now trial and error to find the right r + c?
I notice I can get a pwm signal off many of the pins.
One of the has an irregular pulse, wide, short, wide, short is this a better signal to use?
That looks good. Congratulations!
You get quite varying output anyhow. What do you get if you add the weight?
If the output varies all the time so much you have to increase the capacitor.
I think the resistor value is OK.
You may try the other PWM signals too and check the span and the linearity of the values you get from the K8055.
Make sure that you are not killing the PWM signal of the scales with the 10k + 4.7uF load. You should try to connect only to output pins of the op-amp.
I am having trouble getting the signal to be steady
i think theres a “clock” signal…is that right?
Is the idea to feed the clock signal to a K8055 a2 and only read the analogue signal on a clock pulse?
I cant find a PWM thats as “clean” as the K8055 test, all those off the scale seem to jump around.
does this make sense?
CS Chip Select
CLK Serial Data Clock
DI Serial Data Input
DO Serial Data Output
VSS Ground
NC No internal connection
ORG Memory Configuration
VCC Power Supply
Circuit Cellar article said: “The signal’s low period is directly proportional to the applied weight. (This is conveniently labeled T3 on the DW-36XP scale’s circuit board.) The low pulse is approximately 20 ms wide with no load. It increases by about 2 ms per pound of force.”
If you can’t get steady DC to A1 of the K8055 by increasing the capacitor then the frequency of the PWM signal is not fixed.
Please check the signal’s high period. Is it steady or is there random variation? (Use rising edge to trigger the scope.)
Check also the low period: Is it acting as described: “is approximately 20 ms wide with no load. It increases by about 2 ms per pound of force.” (Use falling edge to trigger the scope.)
About the clock: There may be no help of it. Now it seems that the problem is to measure the time of the low period of the PWM signal.
These are the EEPROM signals (there is no weight data available):
CS Chip Select
CLK Serial Data Clock
DI Serial Data Input
DO Serial Data Output
VSS Ground
NC No internal connection
ORG Memory Configuration
VCC Power Supply