Looking really tidy.
Sound’s like you are doing a good job of fitting 12 gallons of shit into a 10-gallon hat.
BUUUTTT If you want to consider squeezing one more thing in there ( actually it would only be some twin to a switch run externally) Let me explain…
If you put a momentary switch or similar trigger to power on your xEM Access Controller (even though it only draws 11mA ), you will dramatically increase the battery life saving you the need to charge / swap batteries as often; especially if your locking mechanism remains closed without power (if so that will make your wiring even easier) EDIT I just read your earlier thread on the solenoid lock and looked it up on SparkFun, looks perfect for that option.
The only downside I can see for you is finding an ergonomic solution so that you can Trigger and swipe with one hand.
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I have done a similar thing on one of my projects.
I don’t have the math to back me up here, but I"m expecting weeks of runtime under normal usage. I could be very very wrong. I actually considered putting a solar panel on the lid. This was originally for a job that would have had multiple shifts, meaning the lights would be on all night while I was home. The indoor charge rate would be tiny, but so is the draw. What stopped that was knowing that sooner or later, people would start messing with something so obvious.
The only downside I can see for you is finding an ergonomic solution so that you can Trigger and swipe with one hand.
If I were to do that, then I’d probably put a switch on the other side of the box and two hand it. But… It occurs to me that if a person had a lifting magnet, that could be used to close a switch / contacts, so as to power the controller, then cut the power when your hand was removed. The capacitor would hold the relay powered independent of that switch (for a short time). Voila! One handed access with zero (idle) power usage.
I have done a similar thing on one of my projects.
You should definitely verify with testing, but I can show you how you would do the rough calculation.
OUDH-SS-112D Relay has 320Ω coil resistance. That would make the time constant:
τ = R * C
τ = [320Ω] * [2.2F]
τ = 704 seconds
Which means it will take 704 seconds to discharge 63% and get down to 4.44V. The relay will deactivate at 9 volts, which is 25% decay. It’s all exponential and such, so I’m going to use this calculator to get a more accurate result. So it would take 202 seconds to decay below 9V, or 3m22s
Haha, I knew you would ask, I actually put it in this thread ( abridged version ) but deleted it so I didn’t derail this project Thread of yours.
Sample
So my daughter has a sleepout on our property to which I have mounted a pressure pad under the doormat; when stepped on, it powers the RFID Reader (DT Access Controller), which, when swiped *unlocks the door.
*( I have kinda paraphrased this part of the system for brevity and clarity ) There is a bunch more to it, but it is RFID unrelated, I am in the middle of a rebuild of the whole system, I am learning some new stuff (pneumatics) as I go and waiting on parts ( Mostly using Aliexpress so have to wait 3-6 weeks every time I order the wrong thing or forget to order a part )
BUT
I WILL put together something in the projects section when V2.0 is finished.
I did discuss a little of the earlier version in @bepiswriter thread HERE
One note to anyone who tries this. That clear plastic used to make all sorts of storage containers absolutely repels glue. You can let super glue dry on it, then just pick up the solid blob right off the plastic. But… Hot glue guns work great on it. Kinda crazy, but there it is.
I ended up using a 2200uf capacitor. That’s just what I found close in my junk pile. The calculator Satur9 provided (thanks again!) shows a time of 2.6 seconds with this setup. Real world results times just a hair over 1.5 seconds. Were I to redo this, I’d probably grab a 4700uf capacitor. They’re a pretty common value in my pile, and should net a little bit more time.
On second thought, maybe not. The longer it hangs open, the more battery it uses.
And FWIW, the relay I used was a radioshack 275-248. Nothing special about it, I just had a couple. The diode was just something left over from a long ago project.
However, I’m now stuck. I ordered a 12.5V DC charger to use with it, but all the DC power jacks I have access to won’t fit it. I shoulda paid attention when I ordered. So the new charger and matching jack will be here Teusday. I don’t really want to mount anything in the box just yet cause I gotta drill holes to pass wires through still. Oh, well.
I added the LED back, but direct to the board, no wires.
The green and black wires that are coiled up in the upper LH corner are to attach to the solenoid.
The silver item in the same corner of the box is a power input jack for a charger. I may have to add a diode to that later. I noticed the LED on the plug in charger lights up when it’s battery connected. Don’t want it using up my precious battery life. I plan to charge it fully up, then see how long it lasts when opening it a couple times a day.
I only had it half hooked up, when I realized I had power and could register my NeXT. Spent a little time playing with it. Works well at all angles. Works REALLY well if you line up the long axis of the NeXT / attenna coil.
Speaking of which, I think I’m goiing to mount the antenna coil on magnets, so I can position it wherever I like.
For right now though, I’m gonna take the rig over to my buddy’s place and show him my chip works!!!
Whoa. Never thought that through. Just playing with it, I noticed the antenna being on a metal surface cuts the performance down some. Gonna skip the magnets altogether. Good catch, thanks.
Only thing left is to put a little silicone in the ends of the tubing, so the wires don’t chafe on it.
Checked today and the battery was dead. Fortuneatly, the battery management circuit board cuts power when the cells get too low. A couple of seconds plugged in was all she needed, and I was able to access it again.
I have no idea what the state of charge was when I started. Gonna recharge fully, and try again. Then I might try a third time with the charger unplugged just to see if it’s a significant drain.
Now that you have the ergonomics sorted, have you looked for a position to add a momentary switch?
It will dramatically increase the operating longevity!
If you did the momentary switch, You could also put in a battery meter (analog, digital, coloured LED’s, Low voltage buzzer or whatever your preference) to alert/remind you to charge your battery.
I might add a kill switch for use if I know I’m gonna park it for awhile. But… Really trying to avoid adding anything that will detract from the one handed Jedi mind trick aspect of it.
Random thought. Assume my batteries are 2800mah. The controller pulls 11ma while idlling. I shoud get about (2800/11) 254hours of wait time. Or 10.6 days. edited for obvious math error
Does NOT account for power used during periodic reading, or parasitic draw of the charger.
Yeah, in your early post I did a rough working of 9 days for you, before @Satur9 went all beautiful mind on the calculator
A week is GOOD, But (no calcs) a couple of months BETTER.
I have been thinking about a momentary solution for you, difficult without physically standing infront of your toolbox, but the ideas I had were.
a pressure switch like mine but smaller. (they do sell them) but where to install? 160mm x 160mm.
I wondered the obvious like on the floor, but, dirt, damage, moving, so thought about with knee, or if you could put it by the reader but not sure if you could contort you hand enough.
Then I thought, about a capacitive touch sensor ( <5ųA standby) where your hand would “naturally” lie ( Still viable, I might grab one and give it a crack.
I also thought about, a momentary button or the capacitive sensor right on the lid where you would naturally lift it.
so you would.
Totally random thought. Put a momentary switch under the lid, and spring load the lid just enough to keep it up. Movement would be less than 1/8" but doable.
Push down on lid (power on)
Swipe hand (solenoid activated)
Lift lid (power off)
You’d be dependent on the capacitor / relay “hang” time.
Still gonna see if I can do without. The simpler the solution, the less to go wrong.
I was thinking smaller scale for the touch capacitor, pcb stamp size, mounted next to / under reader antenna.
Yes, I thought about switch under the lid also but I was thinking pressure mat, ruled it out for impractibility.
Though your Momentary switch much better idea, smaller and easier to install.
= 
