Re: Voltage, Current and Power monitor - Updated - Part 3

[TJ232]

If you want to quickly add to your project Voltage, Current and Power monitoring capabilities, plus, as a bonus, a proper hardware RTC with integrated Alarm and Timer functions, this might be the extension board that you was looking for:



The modular design will let you to easy connect it and use it with any MCU you want as long as it has I2C bus capabilities and is working in the 3-5.5V voltage range. That includes all the popular existing platforms like Arduino, PIC, ARM, Atmega, ESP8266 and many more!

Original Article about: SmartMon v2.7 Extension Board - Voltage, Current, Power monitor - P1

Available also on Tindie: https://www.tindie.com/products/nEXT_EVO1/smartmonv27ex-power-monitor-for-your-projects/

[TJ232]

Part 2 of the SmartMon v2.7ex series.

    This time we are exploring the Real Time Clock  implementation and we will see how easy or complicated is to set & program the onboard RTC Clock:




Because of the amount of the information, the related main Videos and Articles are splitted in 4 Parts, as follow:

Part1 - General view
Part2 - Real Time Clock driver example
Part3 - INA219 Driver and software implementation example
Part4 - Real World example with Thinkspeak data upload (will follow)

[TJ232]

Finally Part 3 is here: INA219 Driver and software implementation example





Original article: http://www.esp8266-projects.com/2017/03/smart-mon-ext-board-software-example-p3.html

[mariush]

Tantalum capacitors on such a board? why ?!

Be careful about USB and measuring stuff ... ground on usb is connected directly to ground in your power supply and earth ... ideally, you'd want to use some digital isolator like Adum5000 but those chips are maximum 400mW (5v @ <100mA or 3.3v @ 100mA) and about 33% efficient.
Or isolate the i2c communication from the ina219 and power the ina219 from a battery or the measurement voltage or through some isolation transformer or some isolated pol power supply.

And note about plugging a linear regulator in that to-220 location .. i'd like to see how you'd do 3.3v and 3-400mA as you say may be required for the wireless module, from up to 26v ... measure the dissipated power and how it would affect your measurements ... you have 12v in , 3.3v out at 0.3A  .. (12-3.3) x 0.3 = 2.5w of dissipated heat. Impossible without heatsink, and even with a heatsink, the heat may affect your measurements by warming up the current shunt through the pcb and the ina219 chip.

[TJ232]

Tantalum capacitors on such a board? why ?!

Because they are not so bad as you might think. Don't want to start another debate about how evil are tantalum caps. What do you suggest, MLCC only?

Be careful about USB and measuring stuff ... ground on usb is connected directly to ground in your power supply and earth ... ideally, you'd want to use some digital isolator like Adum5000 but those chips are maximum 400mW (5v @ <100mA or 3.3v @ 100mA) and about 33% efficient.
Or isolate the i2c communication from the ina219 and power the ina219 from a battery or the measurement voltage or through some isolation transformer or some isolated pol power supply.

> Good point. Is intended to be used without any USB connection in the field or with a USB isolator port if needed for programming. Power supply is the same so no need for power from USB in such a case.

And note about plugging a linear regulator in that to-220 location .. i'd like to see how you'd do 3.3v and 3-400mA as you say may be required for the wireless module, from up to 26v ... measure the dissipated power and how it would affect your measurements ... you have 12v in , 3.3v out at 0.3A  .. (12-3.3) x 0.3 = 2.5w of dissipated heat. Impossible without heatsink, and even with a heatsink, the heat may affect your measurements by warming up the current shunt through the pcb and the ina219 chip.

> Is designed to place there if needed a Switchmode regulator like the one from the link or similar.   

[Bruce Abbott]

Tantalum capacitors on such a board? why ?!

Because they are not so bad as you might think. Don't want to start another debate about how evil are tantalum caps.

People don't like Tantalums because they short out when over-voltaged or if the polarity is reversed (as if that was a bad thing), but in 40 years as an electronics technician I have only seen one failure that wasn't due to abuse. Al electrolytics OTOH...  and MLCCs are not immune either (I've had to replace a few...).
 

[mariush]

Some tantalum capacitors used to die with actual FIRE leaving crap on the circuit boards. Modern tantalums probably don't behave like that anymore. Like they said, they have problems with overvoltage.

I wouldn't use tantalum capacitors unless I need something that tantalum has, like a predictable low ESR across some temperature ranges or whatever (higher than ceramics and not prone to cracks or microphony or voltage bias, and lower than esr of small capacitance electrolytics, which is usually around 0.3-0.5 ohm and up for < 100uF). 
Electrolytic capacitors are often cheaper and you can simply use capacitors rated for higher voltage (like 63v-100v) because the diameters and heights of such small value electrolytic capacitors are about the same (usually around 5mm diameter , 8-11mm tall) ... and if height is an issue, or you don't want to use surface mount electrolytics, you can place regular through hole electrolytic and lay them flat on the board and optionally - if you really are paranoid - use a drop of glue or for example that thread locker to hold them in place.
You already place the 32 kHz oscillator for the timer chip flat on the board, so it looks to me like you have no issue with that, and there's plenty of room on the pcb.  There also doesn't seem to be any requirement for surface mount only (for example if you want the back of the board to be perfectly flat) as there's lots of through hole parts like the headers and the holes for additional regulator.

Anyway... don't see the attraction of that INA219 chip ... doesn't look that special to me and it's expensive, at around 1.6$ if you buy 100.  It has only a 12bit ADC and not a very good one at that.
You could get a decent 16bit ADC with internal voltage reference like let's say LTC2472 for 2$ (if you buy 100) and you get a 16 bit value every ms or every 4 ms depending on how you configure it... and you put a 0.5$ microcontroller to read the data from SPI and calculate power and all that other crap and push out the values through i2c or whatever you use.

[TJ232]

Some tantalum capacitors used to die with actual FIRE leaving crap on the circuit boards. Modern tantalums probably don't behave like that anymore. Like they said, they have problems with overvoltage.

Yeah, I know the stories. How many have you actually seen yourself? I've seen about 2-3 in 20+ years, in very harsh industrial/telecom/mil environments. And I can bet for at least one case as been a human error.

I wouldn't use tantalum capacitors unless I need something that tantalum has, like a predictable low ESR across some temperature ranges or whatever (higher than ceramics and not prone to cracks or microphony or voltage bias, and lower than esr of small capacitance electrolytics, which is usually around 0.3-0.5 ohm and up for < 100uF). 
Electrolytic capacitors are often cheaper and you can simply use capacitors rated for higher voltage (like 63v-100v) because the diameters and heights of such small value electrolytic capacitors are about the same (usually around 5mm diameter , 8-11mm tall) ... and if height is an issue, or you don't want to use surface mount electrolytics, you can place regular through hole electrolytic and lay them flat on the board and optionally - if you really are paranoid - use a drop of glue or for example that thread locker to hold them in place.
You already place the 32 kHz oscillator for the timer chip flat on the board, so it looks to me like you have no issue with that, and there's plenty of room on the pcb.  There also doesn't seem to be any requirement for surface mount only (for example if you want the back of the board to be perfectly flat) as there's lots of through hole parts like the headers and the holes for additional regulator.

I know that you know that Electrolytic capacitors have a way shorter life than Tantalum ones. And I've seen more of them blow away than Tantalum ones on fire.

Anyway... don't see the attraction of that INA219 chip ... doesn't look that special to me and it's expensive, at around 1.6$ if you buy 100.  It has only a 12bit ADC and not a very good one at that.
You could get a decent 16bit ADC with internal voltage reference like let's say LTC2472 for 2$ (if you buy 100) and you get a 16 bit value every ms or every 4 ms depending on how you configure it... and you put a 0.5$ microcontroller to read the data from SPI and calculate power and all that other crap and push out the values through i2c or whatever you use.

Didn't develop any kind of special attraction for INA219, I usualy prefer other types of INA's to express my attaction about but I found INA219 as a very good and cost effective solution for the intended usage. I am sure that you know very well that they are also other important aspects to keep in mind that pure ADC resolution.