| Electronics > Projects, Designs, and Technical Stuff |
| How does this weight scale power on? (step-on) |
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| langwadt:
--- Quote from: james_s on April 05, 2020, 11:16:49 pm ---Isn't the sensor on those absolute using capacitance? --- End quote --- some yes some have an absolute encoder, but I think most just never turn off, if on with the display off uses a fraction of the battery's self leakage I doub't it makes much of a difference |
| IanB:
--- Quote from: langwadt on April 06, 2020, 03:24:38 pm ---some yes some have an absolute encoder, but I think most just never turn off, if on with the display off uses a fraction of the battery's self leakage I doub't it makes much of a difference --- End quote --- The make and model of caliper makes a huge difference. The cheap "no brand" calipers drain the battery at a phenomenal rate such that you have to remove the battery after use or it will certainly be dead next time you try to use the caliper. With the expensive brands such as Mitutoyo this is not the case and you can leave the battery installed. |
| David Hess:
--- Quote from: amyk on April 05, 2020, 11:21:01 pm ---The ones that "power on" when loaded are actually on all the time, the microcontroller just turns the display off and reduces the measuring frequency in "off" mode, maybe once a second or less. Then when a change is detected it increases the frequency and turns on the display. --- End quote --- That is how I would do it. Most of the power draw is from excitation to the load cell so periodically apply excitation for a few milliseconds, and make a quick low resolution measurement. |
| IDEngineer:
--- Quote from: CharlesK on April 05, 2020, 08:02:58 pm ---How does this scale measure changes and power on without draining its battery? --- End quote --- An excellent question. We have one of those step-on scales, it's well over 10 years old, and I've NEVER changed the battery. I don't even know what kind of battery it has. When you apply a bit of pressure, it CALibrates for a moment and then is ready to go. I haven't paid attention to see what sort of delay exists between the application of pressure and the display responding. If I get some free time (HA!) this is worthy of investigation because even with an ultra-low-power MCU waking up only every couple of seconds, 10+ years on any kind of cell is pretty impressive. |
| IDEngineer:
--- Quote from: CharlesK on April 06, 2020, 11:09:54 am ---I'm trying to get this to work. Is there a way I can check how many ms the arduino wakes while checking the values? this way I could calculate average current draw per second of stand-by. --- End quote --- --- Quote from: mikeselectricstuff on April 06, 2020, 11:18:42 am ---Just set a pin high when awake and look on a scope. --- End quote --- Score another win for "debugging firmware with an oscilloscope". :) One of my favorite questions to ask newbies is to name the most useful tools for firmware debugging. I give a lot more weight to those who include "oscilloscope". |
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