Questions about DSO Shell and proposals
Posted: Sat Dec 17, 2016 9:34 pm
First of all I would like to post, that it was easy to build the 15001 kit. Congratulations, you set up a very good kit! Especially I like that you avoided mechanical switches and therefore placed analog multiplexers!
When trying to calibrate and to run the scope, I've had some difficulties and questions, but also two proposals:
1. getting a "good picture" of a rectangle of more than 10kHz
2. calibrating at internal signal generators' amplitude of 0,1V shows no effect
3. start an aquisition in "single" mode
4. holding a signal with the trigger
5. abnormal spikes shown at battery (operating) voltages higher than 9V
6. abnormal waveforms shown in sec/div ranges that are much "slower" than the measured frequency
7. proposal: operation of two 10440 Li-Ion batteries
8. proposal: "easy" second input with other multiplexer
Why can't I see the frequency of the shown signal, like it is displayed at the DSO 138?
But now to the details: Link to the pictures: https://www.dropbox.com/sh/bue3b5v6p0cf ... SUG0a?dl=0
1.
Already at 4kHz and 5Vss, at 50µs/div and 20µs/div, I see overshoots of more than 1V at the end of the edges in shape of a shark fin. These overshoots do not exist in reality! (see pictures 163.jpg and 88.jpg!) and
What element is responsible for these overshoots? More than this, the switching seems to be much slower than in reality. Unfortunately, this is misleading!
What is the maximum "useful measureable" rectangle frequency? I mean, that it still looks like a true rectangle. 20kHz or even higher? What elements are the first responsible/limiting ones? The 082/084? Or the AD speed of the STM? Would it make sense to replace all 082'/084' by 052's/054's with a faster response and higher slew rate? Or is this nonsense (marginal, compared with other effects)? The measuring interval seems to be around 2µs? This would explain the slow increasing slopes of a "sharp" 10 or 20kHz rectangle which is watched at 10 or 20µs/div. The 10 and 20µs/div are misleading me at a 20Khz rectangle. (See pictures 49.jpg and 887.jpg of 20kHz at 20µs , and even more 644.jpg and 354.jpg at 10µs , ) The last almost realistic looking range seems to be 50µs/div for a 20kHz signal.
I tried to filter away these overshoots with a maximum (30pf) adjusted trimmer: almost no effect. (See picture 233.jpg ) Only with a 180pF capacitor instead of C5 + C6, I got a "helping tradeoff" at 20µs and 10µs ranges. (see picture 411.jpg . Picture 256.jpg is at 1kHz ) At 50µs, the 180pF seems to be a bit retarding, but is still ok for me. Why is the curve shape at 20µs so much different from 50µs? (see pictures 498.jpg and 131.jpg )
2.
I was unable to calibrate the waveform at the 0.1V range of the 1kHz signal; the dc offset of that signal is about 3V, so I had to switch to AC coupling (instead of the instruction manual, where "DC" is shown in the picture). When in AC, turning the Trimmer Caps didn't show a visible effect. It looked quite ok before the calibration trial and so does after. I soldered out the TrimCaps to get to know, where is max and min during a 360° turn. But also this didn't help me. Like said under 1., now, I have a 180pF capacitor soldered instead of C5 + C6.
I tried to find the reason for the 3V DC offset in the signal of the internal 1kHz reference generator. Got to know, that R31 (470 in the schematic) has only 22 Ohms in real. Is that ok? Or by mistake? What would happen, if I would change to 470 Ohm? R16 is 1k, like in the schematic.
3.
From time to time, I see no difference between "norm" and "sing" trigger modes or I am not able to start a single aquisition.
4.
For instance a 120Hz signal: sometimes I am not able to hold it with the trigger. It is rolling through from right to left. The same with a 0.1Hz rectangle (at 2 sec/div).
5.
I got to know, that in fact, the voltage must be significantly less than 9V. From 9V on, I saw negative spikes "down to the bottom" with a 10ms width over all V/div. Even with Gnd coupling! They disappeared at less then 9V Vin. What is the reason for this? In don't think it comes from the LM1117 regulator?!
At 1000Hz 5Vss rectangle and 0.5ms/div and 9V operating voltage, every second, I saw long spikes at the trailing edges (not the leading!) of pos and neg swings (slopes). Is this from an interference with the switching frequency of the ICL7660? Or from "high" voltage? (see picture 407.jpg!). In the 0.2ms/div range I can see this behaviour almost all time, at 0.1ms/dic, I see it all time.
6.
When I watch a 20kHz rectangle at 0.1s and 1s/div ranges, I see extremely misleading artefacts. (see pictures 969.jpg and 46.jpg ) I would expect nothing else but a big beam (balk, bar) (see picture 430.jpg on the comparing scope )
7.
Further, I have a proposal: I think it would be possible to operate the scope with just two "10440" Lithium-ion batteries (accu). It seems, that there is enough space to place such a battery holder between both "back PCBs" (see picture 797.jpg ). You only had to change one plastics part: the back side. The other parts could stay the same! (see picture 440.jpg )
May I operate the DSO from two 18650 Li-Ion cells ( (6.6) 7.0-8.3V)? What issues do you know at voltages less than 8.0V? Does the DSO show a sign, when the Voltage is that low, that it affects the accuracy? Is a power source inner resistance of less than 0.1 Ohm maybe a problem?
8.
Why did you choose a 4053 for the first multiplexer? When another 4051, with a new firmware, we could maybe enable an optional second input channel (multiplexed)! Or is the HC4051 not fast enough to switch between inputs?
Many thanks in advance for your answer!
Best regards, Lars Krueger
When trying to calibrate and to run the scope, I've had some difficulties and questions, but also two proposals:
1. getting a "good picture" of a rectangle of more than 10kHz
2. calibrating at internal signal generators' amplitude of 0,1V shows no effect
3. start an aquisition in "single" mode
4. holding a signal with the trigger
5. abnormal spikes shown at battery (operating) voltages higher than 9V
6. abnormal waveforms shown in sec/div ranges that are much "slower" than the measured frequency
7. proposal: operation of two 10440 Li-Ion batteries
8. proposal: "easy" second input with other multiplexer
Why can't I see the frequency of the shown signal, like it is displayed at the DSO 138?
But now to the details: Link to the pictures: https://www.dropbox.com/sh/bue3b5v6p0cf ... SUG0a?dl=0
1.
Already at 4kHz and 5Vss, at 50µs/div and 20µs/div, I see overshoots of more than 1V at the end of the edges in shape of a shark fin. These overshoots do not exist in reality! (see pictures 163.jpg and 88.jpg!) and
What element is responsible for these overshoots? More than this, the switching seems to be much slower than in reality. Unfortunately, this is misleading!
What is the maximum "useful measureable" rectangle frequency? I mean, that it still looks like a true rectangle. 20kHz or even higher? What elements are the first responsible/limiting ones? The 082/084? Or the AD speed of the STM? Would it make sense to replace all 082'/084' by 052's/054's with a faster response and higher slew rate? Or is this nonsense (marginal, compared with other effects)? The measuring interval seems to be around 2µs? This would explain the slow increasing slopes of a "sharp" 10 or 20kHz rectangle which is watched at 10 or 20µs/div. The 10 and 20µs/div are misleading me at a 20Khz rectangle. (See pictures 49.jpg and 887.jpg of 20kHz at 20µs , and even more 644.jpg and 354.jpg at 10µs , ) The last almost realistic looking range seems to be 50µs/div for a 20kHz signal.
I tried to filter away these overshoots with a maximum (30pf) adjusted trimmer: almost no effect. (See picture 233.jpg ) Only with a 180pF capacitor instead of C5 + C6, I got a "helping tradeoff" at 20µs and 10µs ranges. (see picture 411.jpg . Picture 256.jpg is at 1kHz ) At 50µs, the 180pF seems to be a bit retarding, but is still ok for me. Why is the curve shape at 20µs so much different from 50µs? (see pictures 498.jpg and 131.jpg )
2.
I was unable to calibrate the waveform at the 0.1V range of the 1kHz signal; the dc offset of that signal is about 3V, so I had to switch to AC coupling (instead of the instruction manual, where "DC" is shown in the picture). When in AC, turning the Trimmer Caps didn't show a visible effect. It looked quite ok before the calibration trial and so does after. I soldered out the TrimCaps to get to know, where is max and min during a 360° turn. But also this didn't help me. Like said under 1., now, I have a 180pF capacitor soldered instead of C5 + C6.
I tried to find the reason for the 3V DC offset in the signal of the internal 1kHz reference generator. Got to know, that R31 (470 in the schematic) has only 22 Ohms in real. Is that ok? Or by mistake? What would happen, if I would change to 470 Ohm? R16 is 1k, like in the schematic.
3.
From time to time, I see no difference between "norm" and "sing" trigger modes or I am not able to start a single aquisition.
4.
For instance a 120Hz signal: sometimes I am not able to hold it with the trigger. It is rolling through from right to left. The same with a 0.1Hz rectangle (at 2 sec/div).
5.
I got to know, that in fact, the voltage must be significantly less than 9V. From 9V on, I saw negative spikes "down to the bottom" with a 10ms width over all V/div. Even with Gnd coupling! They disappeared at less then 9V Vin. What is the reason for this? In don't think it comes from the LM1117 regulator?!
At 1000Hz 5Vss rectangle and 0.5ms/div and 9V operating voltage, every second, I saw long spikes at the trailing edges (not the leading!) of pos and neg swings (slopes). Is this from an interference with the switching frequency of the ICL7660? Or from "high" voltage? (see picture 407.jpg!). In the 0.2ms/div range I can see this behaviour almost all time, at 0.1ms/dic, I see it all time.
6.
When I watch a 20kHz rectangle at 0.1s and 1s/div ranges, I see extremely misleading artefacts. (see pictures 969.jpg and 46.jpg ) I would expect nothing else but a big beam (balk, bar) (see picture 430.jpg on the comparing scope )
7.
Further, I have a proposal: I think it would be possible to operate the scope with just two "10440" Lithium-ion batteries (accu). It seems, that there is enough space to place such a battery holder between both "back PCBs" (see picture 797.jpg ). You only had to change one plastics part: the back side. The other parts could stay the same! (see picture 440.jpg )
May I operate the DSO from two 18650 Li-Ion cells ( (6.6) 7.0-8.3V)? What issues do you know at voltages less than 8.0V? Does the DSO show a sign, when the Voltage is that low, that it affects the accuracy? Is a power source inner resistance of less than 0.1 Ohm maybe a problem?
8.
Why did you choose a 4053 for the first multiplexer? When another 4051, with a new firmware, we could maybe enable an optional second input channel (multiplexed)! Or is the HC4051 not fast enough to switch between inputs?
Many thanks in advance for your answer!
Best regards, Lars Krueger