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  • Aug 17 08:29

    bessman on main

    Fix typo in README (compare)

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    bessman on main

    Update workflow to run on new m… (compare)

  • Aug 15 19:56
    CloudyPadmal synchronize #126
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  • Aug 15 06:18

    bessman on legacy

    Initial commit Create LICENSE Added framework for firmware. F… and 60 more (compare)

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    bessman on bootloader

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  • Aug 14 19:28

    bessman on bootloader

    Move bootloader to pslab-bootlo… Move firmware to repository root (compare)

  • Aug 14 19:28
    bessman closed #134
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    bessman on bootloader

    Prepare for repository split Remove drawio flowchart (compare)

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    bessman closed #133
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    bessman synchronize #133
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Daniel aka CyReVolt
@CyReVolt:matrix.org
[m]
Let's say you go to app.pslab.io and then control it via Bluetooth
we'd just need to simplify adding a Bluetooth radio and wire things up :-)
Mario Behling
@mariobehling
This message was deleted
1 reply
Padmal
@CloudyPadmal
@CyReVolt:matrix.org we can also look at the possibility of using WebUSB https://wicg.github.io/webusb/ for connection..
1 reply
I've shared the idea over at #sigrok:libera.chat :-)
RafaelLeeImg
@RafaelLeeImg
After some modification, the oscilloscope works.
I'm reading the python3.9/site-packages/pslab-2.4.0-py3.9.egg/pslab/instrument/oscilloscope.py and power_supply.py
I'm wondering why the abstraction of the two instruments is totally different, why the oscilloscope command is mainly decoded on the PIC24, but power source code sends commands to control I2C bus directly?
Since I'm using two 2-channel DACs on SPI bus, shall I change the abstraction level of the code?
The best practice of abstraction is not overlay between different layers. For example: layer 1, PSLab, layer 2, instrument(oscilloscope), layer 3, (hardware devices MCP4728, ADC, etc).
RafaelLeeImg
@RafaelLeeImg
The newest PSLab desktop version cannot set oscilloscope gain for both V6 and V5, I've changed the voltage range already. Is it not implemented? I've seen python code to change gain, but I cannot verify whether the PSLAB electron app called the function.
RafaelLeeImg
@RafaelLeeImg
I found that the pslab-python is updated, oscilloscope SPI control is added. I'll try with the new one.
Daniel aka CyReVolt
@CyReVolt:matrix.org
[m]
talk for FOSSASIA Summit submitted ✅🥳
Daniel aka CyReVolt
@CyReVolt:matrix.org
[m]
@RafaelLeeImg: see here https://github.com/fossasia/pslab-desktop/blob/development/public/electron.js#L102 to enable debugging with the background processes that are used to talk to the Python library, just set debug: true
RafaelLeeImg
@RafaelLeeImg
20220225-164229-pslab.png
20220226-184840-pslab-ch2-gain2.png
These are 2 screenshots with analog front end error. The problem is fixed today.
2 replies
20220226-234442-pslab-ch1-gain1-OK.png
20220226-234442-pslab-ch1-gain4-OK.png
These are 2 screenshots with gain=1 and gain=4, amplitude is wrong since the circuit is changed. The wave form is correct.
RafaelLeeImg
@RafaelLeeImg
The problem cause the noise is that when the voltage is low, the amplifier creates a negative voltage, that voltage exceed the working range of MAX5400.
20220226-234931-max5400-retouch.png
That limit is due to there are protection diode on the 3 resistor pins, the diode are added by me on the image.
Daniel aka CyReVolt
@CyReVolt:matrix.org
[m]
Interesting :)
RafaelLeeImg
@RafaelLeeImg
Is there any good way to use a different DAC in this project?
The DAC I'm using is MCP4822 which is a 2-channel DAC with SPI bus.
# pslab-python/pslab/instrument/power_supply.py
        self._mcp4728 = I2CSlave(self._ADDRESS, self._device)
        self._pv1 = VoltageSource(self._mcp4728, "PV1")
        self._pv2 = VoltageSource(self._mcp4728, "PV2")
        self._pv3 = VoltageSource(self._mcp4728, "PV3")
        self._pcs = CurrentSource(self._mcp4728)
6 replies
RafaelLeeImg
@RafaelLeeImg
The DAC with in the current configuration, the supply voltage is 3.3V, the full-scale voltage swing by the current supply can be 20mV~3.260V, but the DAC values cannot cover the full-range of the output voltage.
20220301-141802-pslab-DAC-swing.png
RafaelLeeImg
@RafaelLeeImg
The 5V rail is a little bit noisy.
20220301-165421-pslab-v6-5V-rail.png
That makes the oscilloscope noisy with high gain. The image is showed with the gain of 16.
20220301-162724-pslab-v6-gain-16.png
apoorva-raj
@apoorva-raj
Hi, are the Open Hardware and PSLab meetings happening nowadays?
RafaelLeeImg
@RafaelLeeImg
Why does the LM324 use ±10V voltage supply rail while the output voltage swing is only ±5V?
Can I connect it to ±7.5V?Since the LM324 output range is from Vee to Vcc-2V.
1 reply
20220304-162933-pslab-v6-+5V.png
+5V is significantly affected by the switching cap voltage inverter. Since the operating frequency of 7660 is too low. There is no good way to filter this ripple with small capacitors.
I want to use some other ways to generate negative voltage. I want try buck-boost.
RafaelLeeImg
@RafaelLeeImg
The most obvious noise source on each power rail is from the switching capacitor power inverter.
Since the semiconductor industry is evolving rapidly, the era that use low frequency power converter and big capacitors are already faded away.
RafaelLeeImg
@RafaelLeeImg
The calculation value of voltage ripple is quite near the measured result. If I increase the cap to 100uF, the noise will be several mV, that is achievable but the problem is not solved elegantly.
The current of +10V rail is 15mA, measured with DMM.
Voltage ripple = 1510^-3 mA(1/20000 Hz)/(1010^-6 F)=0.075V.
RafaelLeeImg
@RafaelLeeImg
I'm going to modify the ±6V to ±7V by adding a diode to 6.8V zener diode. The good side is to add a reverse PN node which has a negative temperature coefficient to compensate the
I'm considering to change the U10 OPAMP which used for wave generator to ±7V. Thus, I can remove ±10 rail for OPAMPs voltage supply. The output voltage of ±3V can be covered with this configuration.
RafaelLeeImg
@RafaelLeeImg
I didn't find other replacement of MCP4822. I tried to find some MCU with 2 12bit DAC, for example, STM32L431RCT6 the price is OK (around ¥25), but the stock is only like 100pcs. Or, sample-and-hold amplifier is another option, with that, we can reduce the DAC channel to 2 or 1. That leads to some work on firmware.
RafaelLeeImg
@RafaelLeeImg
The MCP4728 has 4 DAC channels, if we can reduce it to 2, we can still have 2 voltage source and a current source, one current source and one voltage cannot controlled independently. Is that OK?
Mario Behling
@mariobehling
Thanks for the suggestion. What is your opinion @CloudyPadmal @bessman @CyReVolt:matrix.org ?
6 replies
RafaelLeeImg
@RafaelLeeImg
I think the reason to have 4 DAC channel is only because MCP4728 has 4 channels and easy to buy. Now, even the price of MCP4822 has rised a lot. In my career, I didn't find any common condition that 4 channel of DAC is required.
There are exceptions, for example, use 2 audio DAC connected as bipolar (BTL) to drive speakers. For 2 channels, it needs 4 DAC. That's only used in very high-end audio amplifier systems.
Daniel aka CyReVolt
@CyReVolt:matrix.org
[m]

Sorry for not having joined the last meetings. I've been a little busy again, about to present something fancy again, today noon at CLT: https://chemnitzer.linux-tage.de/2022/en/programm/beitrag/226

During FOSSASIA Summit, I might be in Berlin, not 100% sure yet. Let me know if you'd like to meet. I'd arrive at the Wednesday, and stay until Sunday evening. Will let you know when it's for sure. :-)

1 reply
RafaelLeeImg
@RafaelLeeImg
I got the new PCB last weekend, this week, I measured all the waveforms and performance on each power rail. Most of the part works pretty well. Including the negative voltage generation part, to replace 7660.
-6.bmp.png
-6V rail, the noise is really low.
5V,10V_SW.bmp.png
The problem is here, the boost converter is working under discontinuous mode, that causes 5V tail near 100mV ripple. This leads to the noise of 3.3V rail and VDDA.
VDDA.bmp.png
RafaelLeeImg
@RafaelLeeImg
This is VDDA, there are around 10mV ripple, not quite good. Since there is no additional voltage reference, this causes noise on the voltage samples of oscilloscope, this will not cause noise on DAC, since the DAC uses internal voltage reference.
The 10V rail consumes 15mA of current, with that condition, I shall use an inductor with larger value. I'm using a 4.7uH now, and I'm waiting for the components to arrive.