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by medicdude
Wed Jun 22, 2016 8:13 pm
Forum: Automation, sensing and robotics
Topic: Raspberry Pi UPS with Auto Restart
Replies: 20
Views: 14522

Re: Raspberry Pi UPS with Auto Restart

Ok I've gone back to my brain and realized that the shunt has a known fixed resistance and the current can be calculated from the voltage drop across it.

Not sure where I went wrong originally XD
by medicdude
Wed Jun 22, 2016 7:32 pm
Forum: Automation, sensing and robotics
Topic: Raspberry Pi UPS with Auto Restart
Replies: 20
Views: 14522

Re: Raspberry Pi UPS with Auto Restart

Also it is my understanding that most multimeters use a current transformer and not a shunt to measure amperage, could be wrong there though.
by medicdude
Wed Jun 22, 2016 7:21 pm
Forum: Automation, sensing and robotics
Topic: Raspberry Pi UPS with Auto Restart
Replies: 20
Views: 14522

Re: Raspberry Pi UPS with Auto Restart

My concern is that calculating amperage from a shunt's voltage drop requires other assumptions (or measurements) about the circuit. If fixed assumptions are used they will change as the battery is loaded or discharged. Since you did not mention anything else in your explanation of the shunt applicat...
by medicdude
Wed Jun 22, 2016 5:25 am
Forum: Advanced users
Topic: Raspberry Pi 3 GPIO Current
Replies: 32
Views: 27977

Re: Raspberry Pi 3 GPIO Current

I found a link to this in some other thread, seems to be about the pi1 http://www.thebox.myzen.co.uk/Raspberry/Understanding_Outputs.html Empirical evidence seems to support what's contained in the pads document; The drive strength setting will guarantee a logical high voltage of at least 1.3V at th...
by medicdude
Tue Jun 21, 2016 1:54 am
Forum: General discussion
Topic: I need to power my Raspberry Pi for 24h without access to ma
Replies: 12
Views: 4385

Re: I need to power my Raspberry Pi for 24h without access t

After some extensive research, I'd like to propose two more battery regulator options! Get as close to 6v with desired battery as practical and use a super cheap 5v LDO Linear Regulator, it will dump excess voltage as heat so not recommended for high-amp continuous usage. Or throw a couple batteries...
by medicdude
Mon Jun 20, 2016 4:17 pm
Forum: General discussion
Topic: I need to power my Raspberry Pi for 24h without access to ma
Replies: 12
Views: 4385

Re: I need to power my Raspberry Pi for 24h without access t

I found the lipo boost converter from above on alibaba, if anyone is interested in building some duct tape 18650 battery packs: https://www.alibaba.com/product-detail/DC-DC-boost-3-7V-to_60473853742.html?spm=a2700.7724838.0.0.eJLqfx For OPs application a 12v lead-acid 'car' battery would probably be...
by medicdude
Mon Jun 20, 2016 6:01 am
Forum: General discussion
Topic: I need to power my Raspberry Pi for 24h without access to ma
Replies: 12
Views: 4385

Re: I need to power my Raspberry Pi for 24h without access t

There is a six cell version of the battery bank available for about $5. Dual USB Power Bank 6X 18650 External Backup Battery Charger Box Case For Phone Oh that's very nice, any details on what battery types that thing can support? It just wired all 6 cells in parallel so I'd only use protected cell...
by medicdude
Mon Jun 20, 2016 5:40 am
Forum: Automation, sensing and robotics
Topic: Raspberry Pi UPS with Auto Restart
Replies: 20
Views: 14522

Re: Raspberry Pi UPS with Auto Restart

I'm concerned your use of a shunt to measure battery current is in-appropriate due to the changing internal resistance of the battery, assuming that you're calculating for current based on a fixed total resistance on the circuit.
by medicdude
Mon Jun 20, 2016 5:23 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: 192khz ADC
Replies: 4
Views: 1297

Re: 192khz ADC

Really confused as to what exactly you're asking here, could you rephrase and/or add more information?
by medicdude
Mon Jun 20, 2016 5:14 am
Forum: Automation, sensing and robotics
Topic: Can someone recommend a popular GSM modem?
Replies: 13
Views: 12528

Re: Can someone recommend a popular GSM modem?

Just did a cursory glance through Amazon and it looks like all "new" GSM usb dongles are around the 40$+ range. If anyone can find a decent new/used product for cheaper, please post it here. Note that your wireless provider may be able to offer you a deal for a 'free' dongle as a new device with con...
by medicdude
Sun Jun 19, 2016 5:46 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Connecting More GPIO
Replies: 13
Views: 2340

Re: Connecting More GPIO

Pull-ups and pull-downs are used to introduce an inherent high or low state to a bus, otherwise it would be 'floating' and have unknown high/low state. "pull-ups" connect the bus to Vcc and result in a 'normally high' state, signals on the bus should tie to ground to force a low condition. "pull-dow...

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