Low cost logic analyzer probe for Rigol MSO5000 EasyEDA project

[tv84]

Show us some pics. 

[S. Petrukhin]

 

[S. Petrukhin]

I recommend replacing R17.
I used 100 Om, but the led was very bright, replace to 5.1 kOm.

[Gandalf_Sr]

Looks good.  The 5.1k LED resistor should allow for 3 or 4 mA of LED current which is good.  Looking at the datasheet for the SN65LVDS1, it says that the Absolute Max Vin is Vcc+2 volts so, with Vcc at 3.3V, you should be OK for 3.3 or 5V logic signals.

I see you have tantalum capacitors on the LDO regulator - I'm not a fan of Tantalums because a) they are expensive and b) they can fail explosively!  Make sure you pick a voltage rating that is at  least twice what you will be operating them at.  If you can replace them with MLCC capacitors, I would make that change - more reliable and cheaper.  There are some aluminum polymer capacitors that can replace tantalums but they are only available for low voltages.

[S. Petrukhin]

Looks good.  The 5.1k LED resistor should allow for 3 or 4 mA of LED current which is good.  Looking at the datasheet for the SN65LVDS1, it says that the Absolute Max Vin is Vcc+2 volts so, with Vcc at 3.3V, you should be OK for 3.3 or 5V logic signals.

I see you have tantalum capacitors on the LDO regulator - I'm not a fan of Tantalums because a) they are expensive and b) they can fail explosively!  Make sure you pick a voltage rating that is at  least twice what you will be operating them at.  If you can replace them with MLCC capacitors, I would make that change - more reliable and cheaper.  There are some aluminum polymer capacitors that can replace tantalums but they are only available for low voltages.

Yes, SN65LVDS1 have tolerant input for 5V. In addition, the logic of 5V TTL never have a logic level" 1 " equal to Vcc, it is always a little less, because this logic is based on bipolar transistors that have a voltage drop at the junction. The ringing of the signal on the fronts is successfully suppressed and dissipated on the input resistors.

I use a lot of tantalum capacitors, ever had a problem. Soviet space and military equipment was saturated with these capacitors. In my opinion, they are good. Here I used only 2 very inexpensive capacitors. I think you needn't be afraid of them. However, the project is open, you can clone it and change the board to any capacitors you like. You can make changes as you wish without restrictions.

[S. Petrukhin]

Friends, I found that the output voltage of 4.5V to power the circuit supplied from the oscilloscope was weak and dropped to 4V at load. It seems that the LVDS driver consumes a little, but there are 16 of them and the total current consumption was about 86mA. It turned out that the drivers due to the voltage drop on the LDO does not receive 3.3V, only 3.0V. But the scheme works steadily. 3V is the permissible supply voltage of the LVDS driver.

[Gandalf_Sr]

The voltage regulator you used, the LM1117 has a dropout voltage (Vin - Vout) of about 1100 mV at 100 mA supply which would explain your not being able to get to 3.3V out.

I used a MC33375ST-3.3T3G which has a WAY lower dropout voltage, around 115 mV at 100 mA and never more than 500 mV, worst case at full load.

I chose my LDOs because they needed to have very low dropout voltages - sorry I missed that aspect when looking over your design.

[S. Petrukhin]

The voltage regulator you used, the LM1117 has a dropout voltage (Vin - Vout) of about 1100 mV at 100 mA supply which would explain your not being able to get to 3.3V out.

I used a MC33375ST-3.3T3G which has a WAY lower dropout voltage, around 115 mV at 100 mA and never more than 500 mV, worst case at full load.

I chose my LDOs because they needed to have very low dropout voltages - sorry I missed that aspect when looking over your design.

Thank you, sir!
I changed the design to use MC33375ST-3.3T3G in the new version 2.1 now.

[Gandalf_Sr]

You're welcome.

[S. Petrukhin]

You're welcome.

I started making an amplifier for built-in generators. The amplitude of 2.5V is very small, I think to make the gain by 2 or 10.
I sometimes need to emulate the sensor signal in industrial 24V equipment.

[Gandalf_Sr]

You're welcome.

I started making an amplifier for built-in generators. The amplitude of 2.5V is very small, I think to make the gain by 2 or 10.
I sometimes need to emulate the sensor signal in industrial 24V equipment.

It's already been done for the MSO5000, on the threads here somewhere.

[EDIT] Here it is https://www.eevblog.com/forum/projects/function-generator-booster-for-mso5000/msg2958594/#msg2958594

[S. Petrukhin]

You're welcome.

I started making an amplifier for built-in generators. The amplitude of 2.5V is very small, I think to make the gain by 2 or 10.
I sometimes need to emulate the sensor signal in industrial 24V equipment.

It's already been done for the MSO5000, on the threads here somewhere.

[EDIT] Here it is https://www.eevblog.com/forum/projects/function-generator-booster-for-mso5000/msg2958594/#msg2958594

Unfortunately, I didn't see it. My idea is to make a board/adapter that simultaneously fits into both the sockets of the built-in generator and the USB connector nearby. You can take power from USB for this device.

[Gandalf_Sr]

I too thought about designing a PCB that plugged into the USB & the 2 BNC connectors but, if you want to use the USB port for more than 1 thing e.g. mouse, USB drive, power for your voltage doubler, your approach will be problematic.  I use SMA connectors so I think a better idea is to build a single PCB that has 2 SMA inputs and outputs, plus a 5-12V power input.  Then you can use SMA-SMA cables with a SMA-BNC adapter at the scope end and choose where the power comes from, either from the USB (directly or via a small hub, which is what I use), or from a bench power supply.

[S. Petrukhin]

I too thought about designing a PCB that plugged into the USB & the 2 BNC connectors but, if you want to use the USB port for more than 1 thing e.g. mouse, USB drive, power for your voltage doubler, your approach will be problematic.  I use SMA connectors so I think a better idea is to build a single PCB that has 2 SMA inputs and outputs, plus a 5-12V power input.  Then you can use SMA-SMA cables with a SMA-BNC adapter at the scope end and choose where the power comes from, either from the USB (directly or via a small hub, which is what I use), or from a bench power supply.

It is not a problem to make an end-to-end USB channel from the oscilloscope's USB connector to the USB connector on the amplifier's PCB.
Along the way we can take away a bit of power for the amplifier. I don't like free-standing boxes.

[Gandalf_Sr]

It is not a problem to make an end-to-end USB channel from the oscilloscope's USB connector to the USB connector on the amplifier's PCB.
Along the way we can take away a bit of power for the amplifier. I don't like free-standing boxes.

Yes, that is a good idea.  One question is to make sure that the 5V supply from the USB connection doesn't bring noise into the amplifiers.

[S. Petrukhin]

It is not a problem to make an end-to-end USB channel from the oscilloscope's USB connector to the USB connector on the amplifier's PCB.
Along the way we can take away a bit of power for the amplifier. I don't like free-standing boxes.

Yes, that is a good idea.  One question is to make sure that the 5V supply from the USB connection doesn't bring noise into the amplifiers.

Will need to take care of filtering the power supply for the amplifier.

[Sharp]

Very good work Petrukhin and the ones supporting you 

What is the next step concerning production ?  Do you have a cheap Chinese company looking into doing the production ?   

[S. Petrukhin]

Very good work Petrukhin and the ones supporting you 

What is the next step concerning production ?  Do you have a cheap Chinese company looking into doing the production ?   

Have not production. This is made for personal use.   

[Michael960]

Hi!

First, thank you very much for this idea!

I need 13.5 V inputs for car diagnostics. So I'm thinking of extend the circuit to arbitrary higher voltages by putting 5V zener diodes in parallel to the inputs and putting 1MOhm resistors in series to this combination of inputs and zener diodes?

Do you see any disadvantages of this?

Best regards
Michael

[S. Petrukhin]

Hi!

First, thank you very much for this idea!

I need 13.5 V inputs for car diagnostics. So I'm thinking of extend the circuit to arbitrary higher voltages by putting 5V zener diodes in parallel to the inputs and putting 1MOhm resistors in series to this combination of inputs and zener diodes?

Do you see any disadvantages of this?

Best regards
Michael

Hi, Michael!

I think 1mOm is a lot. This is not a good idea at all. The logical zero voltage in the 13.5V line may be the logical high voltage in the 3.3V line.
And keep in mind that the voltage of the vehicle's on-board network can reach 14.6V.
it is better to use a voltage divider on two resistors.
And even better use a more advanced and inexpensive also probe from sir Gandalf_Sr https://www.eevblog.com/forum/testgear/ms05000-budget-logic-analyzer-probe-set-design/ This probe can use external threshold voltage.

[Gandalf_Sr]

Thanks for the plug

Sir Gandalf_Sr!  I've been knighted and I never knew!

[S. Petrukhin]

Friends, did someone use a board of my design? Please write a review if you don't mind.

[hydrabus]

Thanks for your work
I have converted it from EasyEDA to KiCad 5.1.7-1 and done a cleanup and rerouting with match length for the signal D0 to 15 (I have done the schematic from scratch too)
The good news is now all is available on KiCad for a version which should work up to 1GSPS (the limit of the MSO5000 LA/TI SN65LVDS1DBVRG4+cables/probes ...).
I have changed some parts also to better parts.
The big plus is I provide also the JLCPCB SMT script to convert the KiCad BOM/POS to JLCPCB SMT BOM & CPL (see JLCPCB_PCBA directory)
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The files are available here http://hydrabus.com/Logic_Analyzer_Probe_Rigol_MSO5000_v2_2_BVE_19Oct2020_KiCad.7z
I have bought 2 unit with full assembly(except LDO and connectors which are not available) and 3 spare PCBs of that design and I'm waiting to receive them in few days

[TurboTom]

Sorry for my ignorance, but I think it would be sufficient to keep the length of the sum of the individual input and output trace of each comparator equal, which would reduce the amount of wiggles and thus possible EMI and "pulse smearing" considerably.

[S. Petrukhin]

Thanks for your work
I have converted it from EasyEDA to KiCad 5.1.7-1 and done a cleanup and rerouting with match length for the signal D0 to 15 (I have done the schematic from scratch too)
The good news is now all is available on KiCad for a version which should work up to 1GSPS (the limit of the MSO5000 LA/TI SN65LVDS1DBVRG4+cables/probes ...).
I have changed some parts also to better parts.
The big plus is I provide also the JLCPCB SMT script to convert the KiCad BOM/POS to JLCPCB SMT BOM & CPL (see JLCPCB_PCBA directory)
(Attachment Link) " alt="" class="bbc_img" />
(Attachment Link) " alt="" class="bbc_img" />
(Attachment Link) " alt="" class="bbc_img" />

The files are available here http://hydrabus.com/Logic_Analyzer_Probe_Rigol_MSO5000_v2_2_BVE_19Oct2020_KiCad.7z
I have bought 2 unit with full assembly(except LDO and connectors which are not available) and 3 spare PCBs of that design and I'm waiting to receive them in few days

You almost completely redesigne the trace, it was a lot of work to put so many wigglings.
I also equalized the length of the output LVDS lines in the first version, but after I saw the photo of the scope board, I realized that this would not give privileges. The Chinese comrades did not even install a load resistor on the LVDS receiver side, let alone equalization differential lines.

I'm not much of a high-frequency expert, but it seem like so much wiggling gives parasitic capacitance and inductance. I checked my version at 50 MHz later. The rectangular signal did not give jitter, the image is frozen. But the triangular signal showed a small jitter, probably a slight deviation in the switching level of the LVDS shapers inputs.

It will be good if you create a project with your version on EasyEDA - it will be convenient for other people to make your version for themselves, which is important for high frequencies.