Oscilloscopes - which is right for what?

[Michael Studio1]

I do have a small Oscilloscope - a DS201 PRO pocket-sized one. By this I mean it is small. Very small - meets (they say) the basic demands of electric furniture repairmen (nothing sexist there . . . is there?) It has a built-in 8Mb flash SD card and rechargeable battery and is connected to the PC by USB. What I can't work out is whether it is intended only for Analog use - or is it suitable for Digital use? How can one tell from the specs? The inbuilt Test Signal is 10Hz - 1MHz (1-2-5 stepping) Size-wise it is a mere 88mm X 59mm X 11mm. and comes in a black velour button-up pouch. It has a probe with hook-revealed tip and normal tip, a GND crocodile clip and USB - micro USB PC connector. The accompanying micro-DVD has, on it, the 15 page User's Manual in English (and other languages)
I need to use an Oscilloscope for measurement or tracing the Digital signals in my Denon AVR-1912E2/EA - in discussion elsewhere on this Forum. Can anyone advise? Michael Studio1 UK 14:06BST 15-05-2018

 

[Harald Kapp]

You can use any scope to trace digital signals. Simply set the voltage range to match the digital signal's voltage and the timescale to get the required resolution. From your description I take it your scope has but one single channel? This is not too great for tracing digital signals as you'll often want to compare timings of different signals with respect to each other (e.g.clock and data). At least 2 channels are imho the minimum for meaningful measurements. The more channels, the better.
Some digital scopes have the option to measure either analog or digital signals in which case the number of digital channels is often much higher than the number of analog channels (easily done by the scope's internal digital architecture). Often you can even measure digital and analog signals simultaneously, Great e.g. for checking the operation of digitally controlled analog circuits. You'll have to shell out a few bucks, however, for those. Currently popular with hobbyists are oscilloscopes made by Rigol. You can even find online instructions how to hack a lower grade Rigol scope so it offers the features of a higher grade one as the hardware is often the same, only a software upgrade is required.

 

[kellys_eye]

Short answer - depends on what you want to do with it.

Long answer - depends on what you want to do with it.

 

[Hopup]

Best bench models for the price: Rigol DS1054Z, Rigol DS1052E/DS1102E. Portable ones, not sure.

 

[Michael Studio1]

You can use any scope to trace digital signals. Simply set the voltage range to match the digital signal's voltage and the timescale to get the required resolution. From your description I take it your scope has but one single channel? This is not too great for tracing digital signals as you'll often want to compare timings of different signals with respect to each other (e.g.clock and data). At least 2 channels are imho the minimum for meaningful measurements. The more channels, the better.
Some digital scopes have the option to measure either analog or digital signals in which case the number of digital channels is often much higher than the number of analog channels (easily done by the scope's internal digital architecture). Often you can even measure digital and analog signals simultaneously, Great e.g. for checking the operation of digitally controlled analog circuits. You'll have to shell out a few bucks, however, for those. Currently popular with hobbyists are oscilloscopes made by Rigol. You can even find online instructions how to hack a lower grade Rigol scope so it offers the features of a higher grade one as the hardware is often the same, only a software upgrade is required.

Thank you Harald for this. You are correct - this DS201pro only has one input. This is the information I am looking for: "You can use any scope to trace digital signals" So thanks again. My hope soars! Please - I am a raw beginner in Digital investigation. The problem here is that I do not know whether the ADC is actually converting or not. So based on your comment: "Simply set the voltage range to match the digital signal's voltage and the timescale to get the required resolution." With what do I measure the digital signal's Voltage? I have two DVM's: a 'HoldPeak HP-9804' and a 'UNI-T UT61-E' (which can be connected to the Lab's PC - but that doesn't make it the better of the two). and - would the Signal be measured at the ADC: (IC30 pin1)[ADINR] to AGND? I shall only be able to measure one Channel at a time, of course. Michael Studio1 UK 16:04BST 16-05-2018

 

[Michael Studio1]

Short answer - depends on what you want to do with it.

Long answer - depends on what you want to do with it.

Thanks, Kelly's Eye - I think we've met earlier in this Saga. And I agree . . ." it all depends . . " Michael Studio1

 

[Michael Studio1]

Best bench models for the price: Rigol DS1054Z, Rigol DS1052E/DS1102E. Portable ones, not sure.

Thank you 'Hopup' I shall check Rigol DS1054Z, Rigol DS1052E/DS1102E. - see how much they are (pats pocket and is unconvinced) and what their specs are like. I am only following (or hoping to follow) a trace of either Left Signal which is 500cps until ADC, or Right Signal which is 700cps until ADC. The idea is to find out why neither Signal is getting to the DAC - that is the DAC isn't showing any signs of them at an Analog Output. It should be a simple thing to do, but I'm not aux-faits with the use of Oscilloscopes in Digital use. Michael Studio1 UK 18:12BST 16-05-2018

 

[Harald Kapp]

With what do I measure the digital signal's Voltage?

Look at the supply voltage of the digital chips. Typical voltages are 5 V or 3.3 V. So a setting of 2 V per division is good for 5 V signals and can be used for 3.3 V signals, too, albeit 1 V per division gives better resolution along the y axis should you be interested in details of the signal voltage.
Other digital signal types exits, too, but are not that common. I doubt you'll find them in your receiver.

would the Signal be measured at the ADC:

Where you measure entirely depends on what you want to measure. An ADC will typically have at least one clock input and one data output. There may also be chip select signals, a data input plus various other signals depending on the digital interface of the ADC.
You may also have to measure the same signal at different points in the circuit, e.g. a data signal at the output of the data source (e.g. the ADC) and at the input of the receiving chip (e.g. a microcontroller) to ensure it is present and unaltered everywhere (like you do with analog signals).

Please don't get confused by the following:
In fact there is no physical difference between analog signals and digital signals other than the interpretation of certain voltages as being logic low (e.g. 0 V ... 0.8 V) and other voltages as being logic high (e.g. > 2.4 V) and the agreement that voltages in between (e.g. 0.8 V ... 2.4 V) aer not valid logic levels. But when you look at high resolution, a digital signal will have to swing between the "allowed" low and high levels and will have to pass the "not allowed" range in between to get from one to the other. It has to do so rather fast, the actual time being defined by the logic family (like for example TTL, CMOS, High Speed CMOS etc.).
Looking at digital signals with a one channel scope, however, makes practically never sense, Most digital systems operate synchronously which means the data are in a defined relation to a clock or other control signals. Analyzing these signals requires to have a time based reference between these signals e.g. to ascertain that valid data is present at a clock edge. Look up e.g. this discussion on logic analyzers.

There's much more to the analysis of digital signals which is beyond the scope of my short excursion.

 

[Michael Studio1]

Look at the supply voltage of the digital chips. Typical voltages are 5 V or 3.3 V. So a setting of 2 V per division is good for 5 V signals and can be used for 3.3 V signals, too, albeit 1 V per division gives better resolution along the y axis should you be interested in details of the signal voltage.
Other digital signal types exits, too, but are not that common. I doubt you'll find them in your receiver.

Where you measure entirely depends on what you want to measure. An ADC will typically have at least one clock input and one data output. There may also be chip select signals, a data input plus various other signals depending on the digital interface of the ADC.
You may also have to measure the same signal at different points in the circuit, e.g. a data signal at the output of the data source (e.g. the ADC) and at the input of te receiving chip (e.g. a microcontroller) to ensure it is present and unaltered everywhere (like you do with analog signals).

Please don't get confused by the following:
In fact there is no physical difference between analog signals nad digital signals other than the interpretation of certain voltages as being logic low (e.g. 0 V ... 0.8 V) and other voltages as being logic high (e.g. > 2.4 V) and the agreement that voltages in between (e.g. 0.8 V ... 2.4 V) aer not valid logic levels. But when you look at high resolution, a digital signal will have to swing between the "allowed" low and high levels and will have to pass the "not allowed" range in between to get from one to the other. It has to do so rather fast, the actual time being defined by the logic family (like for example TTL, CMOS, High Speed CMOS etc.).
Looking at digital signals with a one channel scope, however, makes practically never sense, Most digital systems operate synchronously which means the data are in a defined relation to a clock or other control signals. Analyzing these signals requires to have a time based reference between these signals e.g. to ascertain that valid data is present at a clock edge. Look up e.g. this discussion on logic analyzers.

There's much more to the analysis of digital signals which is beyond the scope of my short excursion.

Thank you, Harald that is an amazingly helpful reply. I shall apply this but I will have to use my single Input DS201pro pocket-size oscilloscope to do so - 'cos that's all I have - even if it makes practically no sense. But before I do so I shall follow the discussion on logic analyzers. Michael Studio1 UK 21:40BST 16-05-2018

 

[bushtech]

Please correct me if I am wrong but at this stage you are just looking for signs of life at certain points along the digital path. What it looks like is unimportant at this stage. Analysis is not required at this stage and a whole new ball game.

 

[Michael Studio1]

Please correct me if I am wrong but at this stage you are just looking for signs of life at certain points along the digital path. What it looks like is unimportant at this stage. Analysis is not required at this stage and a whole new ball game.

 

[Michael Studio1]

Thanks, Dries, you are perfectly right - that is just what I need to do and I am seeking for the correct tool to do the job. All I have (which will possibly do this is) a Single Channel DS201pro Pocket Oscilloscope. Of course the biggest side-issue here is the way this AVR-1912 is constructed. With the pcb's all interconnected and immovable for access with a probe - this is due to some 'protect' feature which turns the AVR OFF should there be any break in connectivity. So no pcb can be checked on the Bench alone - it needs to be connected to the other pcb's. Now, four of these pcb's create a sort of 'stack' which make probing either difficult or impossible. The HDMI_B'D is on the top of the 'stack' and to probe on the underside, in situ, requires the use of an 'endoscope' which I have. This plugs into the Lab pc's Serial Port and, by infinite patience, allows me to 'see' and 'probe' the underside of the HMDI-B'D, on which many of the IC's are positioned, and get a closer look at and 'probe' the AUDIO_VIDEO B'D which forms the bottom of the 'stack'. Looking to place a probe on that 100 pin IC801 on this AUDIO_VIDEO B'D shows the great need for this 'endoscope'.
If I am to successfully proceed with my tracing of any Digital Signal I really have to get advice on whether, for my particular 'is there a Tone there or not' need, my Single Channel DS201pro will 'do'. I do not want to go to the expense of getting a two channel Oscilloscope just for this one-off project.
Which is why I am so grateful to all you guys for the help you are prepared to give. THANKS!! Michael Studio1 UK 11:29BST 17-05-2018

 

[bushtech]

Well, you could take the board out, solder some breakout leads to the points you want to check, plug board back in and start hooking up your scope and testing

 

[Michael Studio1]

Well, you could take the board out, solder some breakout leads to the points you want to check, plug board back in and start hooking up your scope and testing

Yes, Dries, that is what I had been doing early on - remember my 'TaggedTestTails'? They're still there - but you are Very Right to suggest that at this point. This is something (so 73's de Edd said) that he does. I have been using jumper wire - which is really too solid - while he uses strands of CAT 5E Ethernet cable - I will follow suit for already I have had one of my TTT's break away. So I agree, Dries, and will select suitable points to solder TTT's to and get 'with-it'. Michael Studio1 UK 12:47BST 17-05-2018