I'm building a wireless device that have to last with batteries as long as posible. The device has an rf module with a microncontroller that manages the control, that part is bought and works fine. When that module recieves an especific rf signal, has to activate a motor, using a motor driver (LB1930MC).
I'm not a expert in that field, but i achieved this with literaly 5 components (module, 2 capacitors, the motor driver and the connection header for the motor and the JTAG for the module), and that makes me think i'm doing something wrong. If i want to sell it i need a device that is ready for produccion, and i need help in that field. Is something i'm missing?, is something needed in the power part of the circuit or for safety norms that i have to have in mind for production?
And by this I do not mean certification as the FCC for the radio module or anything like that. I mean what is necessary for my product to be a final product, safe and ready to go.
In the power part of the circuit, the microcontroller can work from 3.8 to 1.8 volts, so i'm using 2 AA batteries. If i want to replace it with a lithium battery, i can't because when is fully charged it's voltage is 4.2 volts. The simplest-cheapest conclusion was to put a diode in series with the lithium battery, so now the maximun voltage of the battery drops 0.7 volts (3,5 v), and the minimun voltage of the battery (2.7-3 V for lithium battery) least 0.7 volts is still above the 1.8 minimun voltage of the microcontroller. My question is: a low dropout linear regulator or a DC-DC converter is a better choice for achiving more battery life? (both alternatives are more expensive, and the product needs to be very cheap)
One last question is:
The device needs to run 24/7 countinously forever, so if i use lithium batteries i have to charge it at the same time the device is running.
I read that i can't charge the battery and have a load at the same time because in the constant current part of the charge the current is low and if the device uses more power, the battery keeps discharging and never charges. Achiving this needs an extra circuit that disconnects the battery from the load and powers the load from another source.
The power consumption of my device will be less that 1 mA normaly, with some peaks of current when the rf module is transmiting (the motor is powered from other source).
If i have such low current, that means i can charge the battery and still power the device with no extra components? or is that a risk?
- As i said the average current of the device is less than 1 mA, with peaks of 50-60 mA for the Rf module.
- I have not the option of pluging it into the wall.
- The number of times the device will wake up and activate the motor are from 0 to 10-15 times in a day, with an average of 6-7 times/day.
- I need at least 4 months of battery life (time between recharges).
- I was thinking in using a 500-1000 mA lithium battery.
- The motor used is a little dc motor. It's not dangerous, but the old system that is already used for the motor should continue to function without any problem, so my system must interfere with it as little as possible (in my example only interferes getting in parallel with the motor).