Page 1 of 1
ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Sun Aug 23, 2015 3:15 pm
by Jay Dee
Hi all,
Using an ECIO running on an external USB battery supply. I would like to monitor this ~5v power supply.
I believe for the analogue inputs my measurement can either reference VDD (5v supply) or the Vref+ Pin
Using VDD would not work as that's what I trying to measure, any fluctuation would be cancelled out.
So do I have need to take another voltage ref (I have a small 3.3v reg on the board) and feed this to the Vref+ pin ?
I guess I would need to tweak the Vrefvol value to rescale... but can I still monitor 5v if the Vref+ is only at 3.3v ?
Also, Anyone know what the lower side of this measurment is based on? Vss
I'm sure we used to be able to set the Vref- but this option seems to have gone
thanks, J.
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Sun Aug 23, 2015 5:38 pm
by kersing
According to the datasheet the input voltage should be between Vrefl and Vrefh. So if you are using 3.3V for Vrefh the maximum allowable input voltage would be 3.3V.
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Mon Aug 24, 2015 10:33 am
by Jay Dee
Ah.. Thanks Kersing.. very good point.
If a device is battery powered, its supply voltage will drop as the battery discharges. So Vcc is a pretty poor reference.
Umm.. to monitor this the simplest way would be use the 3.3v ref into the Vref+ pin too give a stable reference and then use a voltage divider on the analog input monitoring the supply voltage. A simple 50/50% voltage divider split would allow the input voltage to rise to 6.6v without exceeding the 3.3V voltage ref.
I think this would work. J.
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Mon Aug 24, 2015 11:06 am
by Benj
Hi JayDee,
That sounds like a good solution to me. Some chips have an internal voltage reference to avoid needing the voltage regulator but the PIC ECIO chips do not have this functionality.
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Mon Aug 24, 2015 8:11 pm
by Steve001
Hi,
I made a network cable analyser for patch leads a few years ago that was battery powered , i used a traco power DCDC Convertor with a 3.5 - 5.5v Input and a 5 volt output then measured the dc battery voltage with a adc pin. just had a look farnell do not list it any more tho ,
Power solve electronics are a distributer for traco and they are very helpful.
http://powersolve.co.uk/
Steve
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Mon Aug 24, 2015 10:24 pm
by Jay Dee
Thanks Steve, handy little brick to give you that buck boost solution. Might be a bit overkill for this project as I'm going down the super small route... well trying too.
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Tue Aug 25, 2015 5:49 pm
by Steve001
you could use a external ref device and a comparator to drive a input maybe ?
have used this device in a battery monitoring device for a low voltage disconnect (admittedly 24 & 36vdc) it is programmable tho
http://www.ti.com/lit/ds/symlink/tl431.pdf
maybe worth a look
Steve
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Tue Aug 25, 2015 8:12 pm
by Steve001
Re: ECIO Voltage Ref- Ref+ for Supply Battery Monitor
Posted: Sun Aug 30, 2015 9:10 pm
by Steve001
here is another 3.5v - 5.0 DC DC Convertor with a 5.0 v regulated output using Maxim parts - MAX Current 250 MA
MAX256ASA+ this is rated at 500 Ma but you will have to change the transformer also
PLEASE NOTE THESE ARE SMD COMPONENTS AND TINY !
Steve