## Friday Free Board Quiz: PCB trace Zo characteristic impedance – prize is OLIMEXINO-32U4 Arduino Leonardo compatible board

OLIMEXINO-32U4 is Arduino Leonardo compatible board with UEXT connector, Arduino connectors, works with Arduino IDE.

And we now add OLinuXino paper Notebook and keychain to all our Quiz winners!

To participate in the Quiz is enough to re-tweet the Twitter Quiz announcement message.

The Quiz question is:

If we have PCB with traces with 65 Ohm characteristic impedance terminated with 10 ohm resistor and we measure the resistance with Ohm meter, what the Ohm meter measurement will show?

You have time to re-tweet and/or answer until Monday 23th of November.

In Monday we will post the correct answer and ask random.org to generate random number in range then announce the winner and ship the board by post/airmail.

Good Luck!

1. 10 Ohm

2. LIME-fan
Nov 20, 2015 @ 22:54:53

As the impedance is frequency related and the ohm-meter measures at 0Hz, the trace has minimal resistance. So the resistance is 10ohms (resistor) plus the resistance of the trace, the via and the solder connection (some 0.1 Ohms) plus the resistance of the plane (0.001Ohms?).

3. What LIME-fan said

4. The meter will show ~ 10 Ohms (The 10 Ohm resistor + negligible trace resistance.) The ohm meter will not measure the initial impedance (which should be around 65 Ohm)

5. ~10 Ohm (10 Ohm resistor + the negligible trace resistance)
(The ohm meter will not measure the initial impedance ~65 Ohm)

6. GeeKen
Nov 21, 2015 @ 08:59:17

Assuming this is a DVM based Ohmeter, it will show Infinite ohms, as a DVM operates & measures in the DC realm. In the circuit shown, the capacitor in the circuit presents infinite Ohms to DC, so the DVM will display “Infinite” ohms – or at least a very high Ohm figure.

The claimed Ohms figures on the drawing only kick in at significant frequencies, as they are not “Resistances”, but “Impedences” (i.e., AC Ohm statistics).

This is a TRICK question 🙂
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7. GeeKen
Nov 21, 2015 @ 09:03:53

I just noticed that that is a Resistor in the circuit, not a Capacitor, so the DVM will show 10 ohms. The 65 ohms will not be involved in the measurement, as per my last post, as that is an “Impedence”. That is the trick item in this question – the term “Impedence” instead of the term “Resistance” gives the game away 🙂

So ignore about half of my last post !

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8. Shouldn’t the question be: Why terminate a 60 Ohm trace with 10 Ohm? 😉

9. Kliment Petkov
Nov 21, 2015 @ 11:13:13

As simple math states the summary impedance should be 140 Ohms, but since the capacitance formed by the two parallel copper tracks Ohm meter have to show infinite or very high value

10. About 10 Ohm. I assume that the trace and the plane DC resistances are less than the Resistors tolerance…

11. indreias
Nov 21, 2015 @ 18:43:32

It’s DC versus AC – as we’ll use an Ohm meter the measurement will show 10 ohms.

12. MiLANCo.
Nov 21, 2015 @ 20:52:35

10 Ohm + some (small) trace resistance

Nov 21, 2015 @ 21:02:41

My ohm meter shows 10.2 ohms.

14. LinuxUser
Nov 22, 2015 @ 01:10:47

If ohm meter would use DC current to do measurements, it would display something a bit above of 10Ohms: 10 Ohms for resistor itself and small extra for trace and ground plane DC resistance, etc.

In case of DC whole process is static and whole meaning of “impedance” downspirals to resistive part. Inductive and capactive parts of impedance make no sense for DC current and do not affect current flow.

15. Marcus
Nov 23, 2015 @ 14:08:15

The 65 ohms characteristic impedance doesn’t matters for the measurements using DC. The display will show 10ohms + DC resistence of the pcb trace.
The DC resistence can only be educated guessed based on the majority of lenghts we already saw on PCBs because, in fact, the PCB trace could be of any arbitrary lenght and still presents 65ohms impedance: think of a spiral on the PCB for example. From our experience we can guess 0,1ohm for the trace.

16. webracerx
Nov 23, 2015 @ 15:16:36

It will be between 45 and 80 Ohms due to typical material
geometries, and if the signal changes layer then the
trace geometry should be adjusted as necessary to
maintain a consistent Zo.

17. Jerry Stuckle
Nov 23, 2015 @ 23:02:48

10 ohms. AC impedance has no effect on a DC resistance.