remove old ecg tutorial

tutorials/ecg/_index.md

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-title: How to use the ECG
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-
-Here's some basic info on how to use the ECG functionality of your card10
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-## Finger ECG
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-![Top View Harmony Board](top_1-4.jpg "Finger ECG and Pulse Oxymeter")
-
-Your card10 comes with a number of fun things to play with
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-  - 1   : Contact,  negative ECG electrode 
-  - 2   : Pluse oxymeter (can [potentially, if at some point supported by software] measure pulse and blood oxygen levels using an optical sensor)
-  - 3   : Contact,  negative ECG electrode (again)
-  - 4   : Screw (also works as a negative electrode, see [8])
-
-
-![Bottom View - ](bottom_5-6.jpg "COM for Bias and positive electrode for finger ECG")
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-  - 5 : COM (for bias)
-  - 6 : Contact, positive ECG electrode 
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-![Side View Details](side_front_7-8.jpg "Pin and isolation")
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-  - 7 : Pin for soldering/stitching an alternative electrode, if you don't want to use (6)
-  - 8 : Plastic distancer, works as an isolation (see [4])
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-## USB ECG
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-  - see [ECG Kit Assembly](../ecg_kit_assembly/) on how to solder your ECG cable
-  -  NB: it DOES matter how you connect the kit via USB. if you get a lot of noise, try to turn the connection
-
-
-Have fun experimenting with the ECG.