I would like it to be removed.
HI,
I haven't fully read through everything but I can say you should look at the requirements / limitations of Vcc, Vin, 5V pin.
My Mini Pro boards has a "raw" pin which accepts 9 to 12 Vdc
and a Vcc pin which is 5V (or 3.3 depending on the board).
Do you have a voltmeter for testing? If not you should get one. It need not be an expensive one. A measurement of the various pins would prove helpful.
From your sketch, the circuit should work with the sensor connected to the regulator. The fact that is doesn't means something is not working like it should or isn't what you think it is. While I think it has something to do with the Vin and Vcc pins there is not enough information to tell.
In your test for sensor operation is the sensor under pressure? Or is it not pressurized (i.e. sensor out should be 0.5V)
I don't think this is an issue but you might want to add a 0.1µF cap near the input of the regulator.
And make sure the 0.1µf cap you have is physically close (i.e. short leads) to the regulator.
Your voltage divider is mathematically correct, however I have two comments.
- Your divider correctly drops 4.5V to 3.3 volts but I believe the analog input range is something less than 3.3 volts, you need to investigate this
- You can multiply both of your divider resistors by 20 or maybe 50 to reduce power consumption. You might want to add a 0.01µ capacitor on the lower resistor. Also I would connect the sensor ground and the lower resistor ground directly to board (for the best measurement). This is opposed to say.. the battery ground.
Good luck
First thing to do is to list (for yourself) the operating requirements. This may sound meaningless but bear with me.
- Battery capacity typically changes with the magnitude of the load, be sure you approximate load matches the curve you are referring to
- What end voltage are you able to accept? The battery curves assume a voltage at the end of life.
The 7ma pin output capacity would be in addition to the board power requirements.
Is you application using the sleep mode at all?
I agree with you battery calculation (given that it assumes the end of life voltage specified in the battery curve.)
You must add the current draw of the regulator to your 0.58ma number. For your regulator it is between 4.2 and 8 ma. I think you should look for a different regulator. Look for a low dropout regulator.
Hope this helps.
Questions are OK, just remember my goal is to help not to do.
Batteries:
If you think about it, battery voltage drops with usage. So the point at which you call "end of life" is when you battery voltage is not enough to meet the input requirement of your project. I looked at the battery you are planning, not much information especially for low power draw applications. Have you looked at using 3 AA or 3 C or 3 D type batteries?
Regulator:
First thing you do is consider the physical regulator (i.e. leaded, soic, sot etc)
Then you look at sources you have access to (R-S, ebay?, .......)
Then you start a small table for the different regulators, I suggest listing dropout voltage and bias current.
Dropout voltage: is the lowest input voltage that will result in the rated output voltage. For you the output voltage is 5V to if your regulator has a dropout of 1 volt, the regulator will start to go out of regulation when its input is ~ 6V.
Bias Current: is the current the regulator needs to operate this will be added to your current budget.
You will likely find a regulator with a lower max current (maybe 100 - 200 ma) will be more suited for you application than the larger ones.
If you want a leaded part but can't find the right device you may have to consider surface mounted parts.
Regarding battery calculation, doesn't it matter that I'm summing up current without considering the voltage? Operating voltage of MKRFox1200 is 3.3v and operating voltage of sensor is 5v.
Not really, if you were calculating power you would have to consider voltage but your battery is rated in mA-hrs. So it is easier to just stay with mA. Keep in mind these are not precise calculations. Even the curves provided for the batteries are only nominal or typical information. The curves change from battery to battery and over temperature etc. Which leads us to "...... for a year....". I suggest you stay with your current goal and see how you make out.
Suggestion:
When you put the processor to sleep you should shut off the sensor. I have attached a schematic however I've not done much work with FET's at 3.3 V so I don't have good suggestion for you. However I expect other members will have a number of suggestions for the semiconductors.
Function of circuit:
MosFets function similar to a relay but they have a "polarity" unlike the relay.
For both Mofets:
Pin 1 = Gate
Pin 2 = drain
Pin 3 = source.
Basic function: then the Gate to Source voltage is 0 then no current will pass from the drain to source (for Nch, would be source to drain for Pch).
When enough voltage exists on the gate relative to the source, the drain will conduct current to the source.
"off' is when no current is being conducted
"on" is when current is being conducted.
So:
When the CPU wakes up, it drives the I/O pin high, the Gate of the Nch is then high allowing the Nch to conduct.
The Nch conducting pulls the Gate of the Pch to ground allowing current to flow through the source - drain to the sensor.
BTW the 1k in series with the Nch gate is not functionally required. I prefer to add it in so if there is a miswire of the Fet you won't cook the CPU.
