{"action":"created","issue":{"url":"https://api.github.com/repos/StephenBlackWasAlreadyTaken/xDrip/issues/93","repository_url":"https://api.github.com/repos/StephenBlackWasAlreadyTaken/xDrip","labels_url":"https://api.github.com/repos/StephenBlackWasAlreadyTaken/xDrip/issues/93/labels{/name}","comments_url":"https://api.github.com/repos/StephenBlackWasAlreadyTaken/xDrip/issues/93/comments","events_url":"https://api.github.com/repos/StephenBlackWasAlreadyTaken/xDrip/issues/93/events","html_url":"https://github.com/StephenBlackWasAlreadyTaken/xDrip/issues/93","id":80899930,"number":93,"title":"Battery voltage measuring circuit may waste >10% battery capacity","user":{"login":"jamorham","id":12565568,"avatar_url":"https://avatars.githubusercontent.com/u/12565568?v=3","gravatar_id":"","url":"https://api.github.com/users/jamorham","html_url":"https://github.com/jamorham","followers_url":"https://api.github.com/users/jamorham/followers","following_url":"https://api.github.com/users/jamorham/following{/other_user}","gists_url":"https://api.github.com/users/jamorham/gists{/gist_id}","starred_url":"https://api.github.com/users/jamorham/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jamorham/subscriptions","organizations_url":"https://api.github.com/users/jamorham/orgs","repos_url":"https://api.github.com/users/jamorham/repos","events_url":"https://api.github.com/users/jamorham/events{/privacy}","received_events_url":"https://api.github.com/users/jamorham/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":8,"created_at":"2015-05-26T10:24:51Z","updated_at":"2016-11-17T16:59:27Z","closed_at":null,"body":"Hi, I was looking at the battery voltage measuring circuit and I think it can be improved. I modified it and it seems to work. Please find my working below and let me know what you think:\n\nThe voltage divider in the hardware_setup.md document uses a 1K and 2.2K ohm resistor. This creates a circuit with 3.2K ohm resistance which is always closed. \n\nAt 3.7 volts this will use 1.15 milliamps constantly (3.7 / 3200). Over 48 hours (typical battery life?) this would be 55 mAh which is >10% of a 500mAh battery's capacity. \n\nChanging these resistors to both be 10K ohm gives a 20K circuit which would use 8.8 mAh over a 48 hour period which is ~1.6% of the battery capacity. \n\nMy tests with these 10K resistors appear to work, with convincing millivolt readings reducing over time for the battery in a 48 hour period.\n\nDepending on the current required/resistance of the ADC on the Wixel, it might be possible to increase these resistors further and get even better power reductions. I haven't investigated this yet. \n\nChanging the resistor ratios means that this voltage divider is now dividing the voltage in half. \n\nThis reduces the accuracy of the original circuit, but has the advantage that batteries up to the 6.5volt the Wixel can support can now be used without overloading the ADC. \n\nIt also slightly simplifies the voltage divider circuit, a builder doesn't have to worry about which resistor is which as they are both the same.\n\nAfter re-soldering these resistors a few times myself, I can't imagine that anyone who has already built an xdrip is going to want to change their existing configuration! But I thought it was worth mentioning as an issue to improve the design and could be even more significant if people wanted to use even smaller batteries.\n\nPlease let me know any thoughts on this. I searched and I didn't find anything implying it had already been covered.\n"},"comment":{"url":"https://api.github.com/repos/StephenBlackWasAlreadyTaken/xDrip/issues/comments/261303877","html_url":"https://github.com/StephenBlackWasAlreadyTaken/xDrip/issues/93#issuecomment-261303877","issue_url":"https://api.github.com/repos/StephenBlackWasAlreadyTaken/xDrip/issues/93","id":261303877,"user":{"login":"detroitdr","id":23529075,"avatar_url":"https://avatars.githubusercontent.com/u/23529075?v=3","gravatar_id":"","url":"https://api.github.com/users/detroitdr","html_url":"https://github.com/detroitdr","followers_url":"https://api.github.com/users/detroitdr/followers","following_url":"https://api.github.com/users/detroitdr/following{/other_user}","gists_url":"https://api.github.com/users/detroitdr/gists{/gist_id}","starred_url":"https://api.github.com/users/detroitdr/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/detroitdr/subscriptions","organizations_url":"https://api.github.com/users/detroitdr/orgs","repos_url":"https://api.github.com/users/detroitdr/repos","events_url":"https://api.github.com/users/detroitdr/events{/privacy}","received_events_url":"https://api.github.com/users/detroitdr/received_events","type":"User","site_admin":false},"created_at":"2016-11-17T16:59:27Z","updated_at":"2016-11-17T16:59:27Z","body":"Syntaxerr66, Thank-you for sharing, I'm currently working on one of these for my son. I can only find 5% resistors not 1%. Will that matter? Can i use the 5% resistors?\r\n\r\nThank-you in advance,"}}
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