# Puck.js as power meter logger

• Hi and thank you for great links!
There is only one puck.js smart meter example https://www.espruino.com/Smart+Meter that I found.

Apart from the LDR, there are no other components. The idea is that it will wake up to send out a reading every hour (as a baseline)

• Sun 2021.06.20

Thank you @user130485 for the link which assists in locating the appropriate datasheets.
Following the 'Light Dependent Resistor' link takes us to:

As all show a wide range of voltages permissible, we will mainly be concerned with the power rating, which is 100mW max.

As there are no other parts in the circuitry, we will mainly be concerned with the resistive value. Since from Ohm's law E = I * R we may deduce the the formula for current,
I = E / R and using the values provided in post #1, we learn that the higher the resistance, the lower the current draw and thus a lower power consumption. P = I * E

``````Light resistance: 450K-1.2M
Dark resistance: 10MΩ

E=IR  I=E/R  3/450K = 6.67 e-6
P=IE  *3 = 0.000 020

Light resistance: 5kΩ-10kΩ
Dark resistance: 0.5MΩ

I=E/R  3/5000 = 0.000 600
P=IE   *3 = 0.001 800
``````

The lowest resistive component is nearly 100 times worse in power consumption.

In conclusion it can be observed that from the values given, the LDR with the highest resistance will consume the least amount of power, but for those characteristics, will most likely be the highest cost.

Even the worst case part will only consume 2ma for a fraction of a second, every few seconds. So compared with every thing else going on, is a negligible loss.

That said, it must also be known that the internal resistance that the LDR will be in circuit with is around 13K ohm.

http://www.espruino.com/datasheets/nRF52­832_PS_v1.0.pdf
See: p.151 section 20.4.1 GPIO Electrical Specification

Review the datasheets for best characteristics and then compare part cost.