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Research question

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Could a single poor contact (so not a full disconnect), between the copper pads of a 16Gb SDHC-card and the internal card slot of a Canon Powershot SX 270 HS camera, exactly reproduce the “missing IMG_509” end-state situation ?

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This end-state is achieved when:

  • an image number x is skipped and is nowhere to be found on the SD-card;

and

  • the last memory cluster of image number x-1 and the first memory cluster of image number x+1 are contiguous.

I use the words ‘photo’, ‘picture’ and ‘image’ interchangeably.

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TEST SET-UP

Canon Powershot SX 270 HS

Firmware: 1.0.2.0, June 4th, 2013

Factory settings

SanDisk 16Gb

SDHC Ultra

DIP-switch

10 x

SDHC extension cable

(cut in half, circuitry on next page)

USB smartcard

reader

SDHC extension cable

Jopto 18.9 "48 cm

Various

Software tools

PC /

Laptop

1KΩ

Potentiometer

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CARD

READER

EXTENSION CABLE CIRCUITRY

DIP-switch

(all others closed)

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2

3

4

5

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7

8

9

1

2

3

4

5

6

7

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10

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14

15

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

CARD

Flat cable

1 KΩ

Potentiometer subsequently

“bridges” the single open dip switch

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TEST APPROACH

ALL SWITCHES CLOSED

OPEN 1 SWITCH, BRIDGE BY POTMETER AT 1KΩ

SWITCH CAMERA ON

CHECK ERROR MESSAGE (STILL) APPEARS

=

“Memory card error”

SWITCH CAMERA OFF

DECREASE POTMETER RESISTANCE A BIT

NOTE POTMETER VALUE FOR THIS SWITCH

YES

NO

NOTES

  • Pin 4 and 7 are both ground and I skipped these.
  • After reaching the critical resistance point up to which the error message persists, I checked whether I could skip a picture this way by putting the potmeter at 0KΩ, switching the camera on, turning the potmeter above the critical resistance point and taking a picture. This always skipped a photo.

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TEST RESULTS

These are some SD cards I used. Looking at the sharp scratches on the copper pads, it looks like the reader inside the camera has some needle-like pins that cause a point contact.

https://en.wikipedia.org/wiki/Contact_resistance

increases the poorer the contact. The table shows above which resistance threshold, the error message “memory card error” will be

displayed for each pin.

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INTERPRETATION OF RESULTS & CONCLUSION

INTERPRETATION OF RESULTS

1) I struggle to find a good benchmark value for the resistance threshold of a poor contact (instead of a total disconnect)

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2) We do know that the reader connection with the SD card is ‘point sharp’, so the actual copper contact will be like a rather ‘thin’ wire hence having a relatively high resistance that could increase/decrease due to mechanical shocks.

CONCLUSION

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A poor SD-card contact can be defined as a certain contact that has a resistance between a specific threshold (few hundred Ω) and a total disconnect. Any contact ending up in this state affirms the research question.

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It is difficult to assign a probability to a contact being poor as the result of a camera fall, compared to a total disconnect as the result of a fall. Intuitively though, a poor contact seems to have a much broader range of resistance states to end up in, than a total disconnect. Ideas/suggestions welcome.

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