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| MS05000 Budget Logic Analyzer Probe Set Design |
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| Gandalf_Sr:
Here's an updated (vn2) set of build notes. [EDIT] OK, who spotted my (ahem) deliberate typo in that I run my soldering iron at 28 degrees C? It should be 280 C. |
| Gandalf_Sr:
bigboss59 I am trying to send you PMs but it tells me your inbox is full. FYI, I can ship to France. For others, I have figured out how to send to France, Sweden, Portugal, UK, Australia for a reasonable rate (with no tracking or insurance) so I can send PCBs for the prices I already stated. The USPS web site lists countries that they will not ship to at the moment but the above are not on that list. PM me if you're still wanting PCBs. |
| Gandalf_Sr:
Some of you will be getting the bare boards soon, here's a few notes on the circuit that may come in useful... Connector PCB Align J1 before soldering then solder just 1 pin and check it's straight. IF IT ISN'T STRAIGHT, DO NOT TRY TO BEND IT STRAIGHT or you will lift the pad. Heat the 1 soldered leg and realign. Once it's aligned properly, solder the other legs. Probe PCB Be careful fitting VR1. I over-temped one and it was damaged and gave lumpy control of Vadj. Best practice is to turn VR1 upside down and tin the bottom of the leads; then tin the 3 pads on the PCB and carefully sweat it down 1 leg at a time. Protection circuits. PTC on the Connector PCB There's a positive temperature coefficient (PTC) device on the bottom side of the connector PCB. The Probe boards draw all their power from the +4.1V supply via the PTC but PTCs have a fairly high resistance and using one will limit how much current you can draw from the downstream +3.3V (300 mA max limit of the LDO per Probe PCB) and Vadj (100 mA max limit of the Vadj LDO per Probe PCB) supplies - so, in theory, you could draw 800 mA total from the MSO5000 which you would never achieve using a PTC. Also, I don't know what the current limit is that can be supplied by the MSO5000 4.1V line; the PTC will limit total current to under 500 mA. However, if you put the listed ferrite bead on the connector PCB in place of the PTC, you will get whatever the MSO5000 can supply. I've tested that the LA works with both a PTC and a ferrite bead but I haven't done limit tests yet. Probe PCB Overvoltage Protection D2 is a 3.9V Zener on the 3.3V rail, if the 3.3V rail is taken above around 3.6 volts (should never happen) this Zener will ground the 3.3V supply. D3 is a 3.9V Zener connected to the Vext pin via R8, a 47.7 Ohm 0.25 Watt resistor. If you're building the 5V version, D3 is a 5.6V Zener and may trip as low as 5.3 volts which may cause issues if you're using an over-voltage 5V logic input at say 5.2V (check the range in the diode's datasheet). If this is a problem, you can either put a higher voltage Zener as D3 or leave D3 off the PCB and have no protection other than the 47.7 Ohm resistor. If you want to supply the device under test with more than a few mA of current and you're using Vext to supply the DUT, be aware that R8 will reduce the supplied voltage; however, you can supply the device under test from the Vadj or +3.3V pins (device shutdown limits are 100 mA or 300 mA) on the 3-pin header just above the switch. R21 (100k Ohms) R21 is provided to pull Vcca down to zero when there's no power. I found that Vcca would stay on for seconds at a time without R21, probably because the voltage level translator (VLT) IC draws so little current. The ACX (3.3V) version of U1, the VLT, is most susceptible to this effect although it's not really an issue, I just didn't expect U1 to operate with no Vcca supplied. |
| NoisyBoy:
Hey Gandalf_Sr, I have been watching your project since your inception during your cruise, but I did not have time to participate. Nice work and that was done really fast! Great work and thank you for all your kind contribution to the community. I am many here will benefit from it without having to pay the high price for the Rigol probe. |
| Gandalf_Sr:
Thanks, that last cruise was just in the nick of time before the whole shut down kicked in. I'm still getting requests for PCBs. |
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