What The FX Pocket Chrono Should Have Been - Rechargable
- Thread starter heavy-impact
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I have the same set-up here. The Shooting Chrony Beta Master hasn't been out of the box in years. I also 3D printed a mount for the FX Radar to use connected to my M3 Impact's extended rail, so don't even have to worry about lining it up on the barrel.
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So I finally got some time to work on this project. The end design wasn’t exactly what I’d envisioned originally but it came together pretty well.
My original plan was to make the “battery tray” part of the lid so I’d just have 1 unit. After digging in to this, that proved to be impossible because the negative springs are on the right of the unit and the tabs for the cover are on the top.
I used battery spacers from Amazon for my connections mainly for aesthetics. I need to solder my USB cord (also Amazon) to the spacers and power everything up this evening. From a visual standpoint, I don’t see any issues with connection and the existing springs hold tension on everything.
My original plan was to make the “battery tray” part of the lid so I’d just have 1 unit. After digging in to this, that proved to be impossible because the negative springs are on the right of the unit and the tabs for the cover are on the top.
I used battery spacers from Amazon for my connections mainly for aesthetics. I need to solder my USB cord (also Amazon) to the spacers and power everything up this evening. From a visual standpoint, I don’t see any issues with connection and the existing springs hold tension on everything.
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Got the leads soldered in, plugged the battery pack in, crossed my fingers and……..GREEN LIGHT!!!
I have a 5v wall wart to either charge the batteries or power the unit directly. I also verified that the output on a USB on my laptop is 5vdc so now I have 3 ways to power the unit (4 if you count batteries)
The unit installs just like a power brick in mobile HAM radios (where I got the idea from and another of my long list of hobbies) so if there was an issue, pull the adapter, replace the back cover with the factor cover, box it up and send it off.
I have a 5v wall wart to either charge the batteries or power the unit directly. I also verified that the output on a USB on my laptop is 5vdc so now I have 3 ways to power the unit (4 if you count batteries)
The unit installs just like a power brick in mobile HAM radios (where I got the idea from and another of my long list of hobbies) so if there was an issue, pull the adapter, replace the back cover with the factor cover, box it up and send it off.
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I finally got the courage to haul my test equipment out in the 20F temps that we are having right now. This post is going to be pretty long because I found out a lot about the FX Chronograph today.
Here is the basic "circuit".
Basically, I just have a variable power supply (That was REALLY NOT HAPPY to be outside) in the cold that is powering the FX Chronograph. I have a 1.15Ohm resistor between the Chrony and ground so I can monitor the current through the circuit. The Scope is across this resistor, so mV basically equals mA. I then have my DVM across the power leads to the Chrony so I can see exactly what voltage is going to the chronograph minus the voltage drop across the 1 Ohm resistor.
Here is the scope on top of the power supply. I current limited the power supply to 100mA, just in case.
Add the gun, and we're ready to test:
Here is the waveform from turning on the Chronograph:
This is 10mV per division, so this is pulling just under 20mA after start up
As soon as you connect the app, you get this waveform:
This is at 50mV per division, so the system is drawing about 70mA when running. Note the huge spike in current. That is at least 300mA for a second!
After it is connected, it gives this waveform:
This is a lot faster acquisition at 2mS per division horizontally. There are a couple of consistent spikes in the current that my scope was triggering off of, but these have nothing to do with detecting shots. This says that we are pulling 76.5mV RMS, so this is the DC Voltage. Since I have a 1.15Ohm resistor,
This means that the FX Chronograph is pulling 66.5mA all the time (76.5mV/1.15). I did a WHOLE LOT of testing, and I have determined that there is no instantaneous change in current when there is a shot detected. I tried different trigger levels, acquisition speeds, etc. It is running "full blast" when you have the app open. This is the same as when you close the app to answer a call or something, as soon as you minimize the FX app, the current draw drops back down to 20mA while it is waiting to reconnect.
@txcomp mentioned to me that he was seeing issues when the Chrony received 5.1V or above, so I tested that too. This is where it gets interesting. There is a pretty significant increase in the background noise on the baseline when the voltage was turned up to 5.15V. I didn't see this consistently at 5.1V, but I did at 5.15V:
It was still reading when at this voltage, but there is obviously something different going on, so I wouldn't recommend it!
Turing the voltage down to 5V, here is what you get:
Note that the current draw went up when the voltage was dropped, just as @nervoustrig observed. It is 76.8mV now where it was 72.2mV at 5.15V.
Dropping it down to 4V gives the following:
We are now at 86.7mV. Divided by 1.15, we are pulling 75.4mA
Finally, when I was supplying 3.75V to the Chronograph, the app was saying that it was 3.66V and was at 10% battery capacity. Everything appeared to be working, but it wouldn't read my shots at this level:
Note that this is 88.8mV, so our current draw is 77.2mA at the maximum that I measured.
So, there are the results of my testing. Below about 4V the chronograph loses it's mind. Above about 5.1V, the chronographs behavior changes, so I don't recommend running it that hot. There is no discernable difference in the current draw during a shot event.
Happy shooting!
Jonathan
Here is the basic "circuit".
Basically, I just have a variable power supply (That was REALLY NOT HAPPY to be outside) in the cold that is powering the FX Chronograph. I have a 1.15Ohm resistor between the Chrony and ground so I can monitor the current through the circuit. The Scope is across this resistor, so mV basically equals mA. I then have my DVM across the power leads to the Chrony so I can see exactly what voltage is going to the chronograph minus the voltage drop across the 1 Ohm resistor.
Here is the scope on top of the power supply. I current limited the power supply to 100mA, just in case.
Add the gun, and we're ready to test:
Here is the waveform from turning on the Chronograph:
This is 10mV per division, so this is pulling just under 20mA after start up
As soon as you connect the app, you get this waveform:
This is at 50mV per division, so the system is drawing about 70mA when running. Note the huge spike in current. That is at least 300mA for a second!
After it is connected, it gives this waveform:
This is a lot faster acquisition at 2mS per division horizontally. There are a couple of consistent spikes in the current that my scope was triggering off of, but these have nothing to do with detecting shots. This says that we are pulling 76.5mV RMS, so this is the DC Voltage. Since I have a 1.15Ohm resistor,
This means that the FX Chronograph is pulling 66.5mA all the time (76.5mV/1.15). I did a WHOLE LOT of testing, and I have determined that there is no instantaneous change in current when there is a shot detected. I tried different trigger levels, acquisition speeds, etc. It is running "full blast" when you have the app open. This is the same as when you close the app to answer a call or something, as soon as you minimize the FX app, the current draw drops back down to 20mA while it is waiting to reconnect.
@txcomp mentioned to me that he was seeing issues when the Chrony received 5.1V or above, so I tested that too. This is where it gets interesting. There is a pretty significant increase in the background noise on the baseline when the voltage was turned up to 5.15V. I didn't see this consistently at 5.1V, but I did at 5.15V:
It was still reading when at this voltage, but there is obviously something different going on, so I wouldn't recommend it!
Turing the voltage down to 5V, here is what you get:
Note that the current draw went up when the voltage was dropped, just as @nervoustrig observed. It is 76.8mV now where it was 72.2mV at 5.15V.
Dropping it down to 4V gives the following:
We are now at 86.7mV. Divided by 1.15, we are pulling 75.4mA
Finally, when I was supplying 3.75V to the Chronograph, the app was saying that it was 3.66V and was at 10% battery capacity. Everything appeared to be working, but it wouldn't read my shots at this level:
Note that this is 88.8mV, so our current draw is 77.2mA at the maximum that I measured.
So, there are the results of my testing. Below about 4V the chronograph loses it's mind. Above about 5.1V, the chronographs behavior changes, so I don't recommend running it that hot. There is no discernable difference in the current draw during a shot event.
Happy shooting!
Jonathan
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Your testing goes well beyond my rudimentary knowledge gained from my RC hobby. I have some 380mah 1s LiHV batteries that are rated at 60C discharge. Based on what I'm reading, the batteries should be able to handle the current draw without a sweat, but my useable voltage range would be from 4.35v down to 4.0v, instead of the usual 3.8v that I discharge my batteries to. I'm unsure how to calculate the runtime I'll get from a 380mah pack though. I'm not one of those guys that has the chrony on all the time for bench shooting; I only use my chronograph in short spurts for tuning. So even if the pack only gives me 15 minutes of battery life, the convenience of using batteries I already have and are rechargeable would be worth it to me.
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You have a 380mah battery pack, so that is your "gas tank". You can drive 380mA for one hour with that battery. The FX Chronograph is pulling roughly 77.2mA when in normal operation, so you can theoretically divide 380 by 77.2 and say that you will get around 5 hours of run time from that battery. This said, there are voltage levels on the Chrony that are higher, so you will almost certainly get a good bit less than that. I would knock 20% off of that and say that you can probably get 4 or so hours from that battery.
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Thank you for explaining that. I'm a little confused, cause doesn't the voltage drop as you use up that 380mah capacity? So using all 380mah wouldn't mean you've drained the pack to 0.0v?
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It's no problem. I've spent a lot of my career studying batteries (Yea, I'm great fun a parties
) Li-Ion batteries don't discharge in a linear fashion. Here is a typical discharge curve:The discharge curve for Alkaline is more linear than this, but this non-linear curve is what makes Li-Ion so useful. You'll notice this with a Li-Ion drill. They will just quit instead of slowing down like the old Ni-MH batteries did.
The manufacturers aren't really consistent with how they test these numbers, but none of them go to "0".
The fact that the FX Chrono gives up below 4V would be bad for this typical curve, but your batteries sound like they should do just fine and that they are already considering 4V to be the "discharged" voltage.
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Really appreciate you taking the time to explain that! So many intelligent people on this forum that give of their knowledge freely.
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Sorry to double post, but does anyone know if magnets mess with the radar that this thing uses to measure the projectiles? Since I'm converting to LiHV, and LiHV batteries don't like to sit around at any voltage other than their storage voltage, I'll be taking the battery hatch on and off regularly. I'd like to drill for some tiny magnets to make the hatch magnetic on/off.
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As you can tell, @SkeeterHawk is the electronics guy between the two of us. I'm more the wood/plastic fab guy. We're VERY dangerous when we start brainstorming together though! 
I ordered an adjustable buck that has an input range of of 3 VDC - 32 VDC and an adjustable output range of 1.25V - 30V to experiment with. If it's small enough, which I believe it is, I can design it in to the cover. If that works, you can basically take most any DC power source (except maybe a Tesla car) and run the unit. Yes, it's overkill but I truely enjoy driving finishing nails with a 2lb sledge hammer.
I ordered an adjustable buck that has an input range of of 3 VDC - 32 VDC and an adjustable output range of 1.25V - 30V to experiment with. If it's small enough, which I believe it is, I can design it in to the cover. If that works, you can basically take most any DC power source (except maybe a Tesla car) and run the unit. Yes, it's overkill but I truely enjoy driving finishing nails with a 2lb sledge hammer.
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That is a REALLY cool idea but unless the circuitry is shielded, which I doubt it is, it's probably going to mess with it. @SkeeterHawk has been inside his and knows what to look for so he would be better to answer than I would be. I'm planning to put a small threaded brass insert in mine and use a machine screw with a large knob to replace the "where in the hell did that thing go now!" screw that it came with.
Harbor Freight has these little (like 8mm) rare earth magnets that are CHEAP ($2.99 for 10). I keep a couple of tubes around the shop just to play with. They're thin too so those would be ideal.
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My gut feeling here is to say No. Even though there is no shielding on this unit at all (Except for ground planes on the boards, but that is a stretch), I don't think consistent magnetic flux being present will mess with the detectability of the unit as long as they aren't on the front. That said, I would tape a few onto the chassis (more than you plan to use) where you plan to mount them before permanently mounting them just to make sure.
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Wow. Going by this information my external pack should last for about 130 hours!
That's including the 20% knock off.
Mine is from the ATN Scope I use to have. It's 200000mah @ 3.7V and 130000mah @ 5V
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