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Based on a question I asked earlier today, I am trying to verify that there's not short caused by my bad soldering.

Luckily I had bought two of these modules. To make a baseline, I started looking at the module that I had not done anything to.

Using this Multimeter (on a disconnected module -- it has no solder and no wires in/out), I am pressing the black lead again the MOSI pin (see diagram below) and moving the red lead one pin down, one pin at a time.

However, I am not entirely sure what I am looking at, for example:

With black on MISO and red on MOSI, or SCK, the reading is 350+K Ohms.

With the black on MISO and read on RESET, the reading is 150+K Ohms.

With black on MISO and red on DIO5, the reading is 1.05K Ohms and red on GND shows 0.5K Ohms.

When I compare that with this video for example, his reading stays at 1 across pin changes.

Again, this is an untouched board, direct from the seller. So is my understanding not correct (i.e. the readings are fine and I don't know what they mean)? Or is it a bad module?

enter image description here

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  • \$\begingroup\$ Can you inspect visually ? \$\endgroup\$
    – Long Pham
    Jun 25, 2018 at 3:44
  • \$\begingroup\$ @LongPham What do you mean? \$\endgroup\$
    – Sam Hammamy
    Jun 25, 2018 at 3:45
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    \$\begingroup\$ If you have a short you will most likely get about 0 ohms. \$\endgroup\$
    – user253751
    Jun 25, 2018 at 3:59
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    \$\begingroup\$ Because there's stuff on the board, which has connections between the two pins, and you get bogus resistance measurements because it's not designed to have a particular resistance. That's generally what happens when you try to measure the resistance of ICs, diodes, transistors etc. It doesn't mean there's damage. The point is it isn't 0 \$\endgroup\$
    – user253751
    Jun 25, 2018 at 4:51
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    \$\begingroup\$ The "1" you see on the video will be on the lowest resistance range, probably 200 ohms, or "continuity test", which usually sounds a buzzer below some value, 5 or 10 ohms. ALL your measurements are above 200 ohms so you'd see "1" on your 200 ohm range. \$\endgroup\$
    – user16324
    Jun 25, 2018 at 10:16

2 Answers 2

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None of these are shorted, which is what you read when the DMM leads are connected to each other.

With black on MISO and red on MOSI, or SCK, the reading is 350+K Ohms.

MOSI and CLK are both high R inputs as displayed

With the black on MISO and read on RESET, the reading is 150+K Ohms.

Reset is high R input as displayed

With black on MISO and red on DIO5, the reading is 1.05K Ohms

Both are low R outputs but not active? probably diode resistance

and red on GND shows 0.5K Ohms.

Same as above

Unless you wore a gnded ESD strap, they were not untouched

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It's most likely fine. These kind of numbers are typical when there are components on the board. You might want to trace through and see what that 500R reading is - perhaps a resistor on the board. A short from bad soldering is generally pretty close to zero ohms.

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