Sunday, 15 January 2017

DIY Chrono Mark II

Well it's been a long time since I started off this project and I've made a few changes along the way and a few people have had a go at making their own Chronos based on the entries in this blog, some followed the design and some incorporated elements of their own into the design to improve it.
Chrono Mark II Assembled
There were a couple of the things I wasn't keen on with my design: -
  • The fact that it was not a round tube but a teardrop and therefore may not always line up with the rifle and look a bit odd.
  • An external charger circuit was required to charge the internal battery.
  • The switch was mounted at the other end of the tube from the electronics and was a bit of a pain to wire up and assemble.
So along came the Mark II with the intention of improving on those issues.

The main reason for the teardrop design was to fit in the electronic modules with the central tube so I needed to come up with a design where I could place the modules and battery around the perimeter of the tube whilst keeping the overall diameter as small as possible.

I also wanted to add a charging circuit inside the tube so there was only one part to worry about so you could just plug it into a phone charger to charge it.  If I could get all this inside the tube, along with a switch located at the same end as the electronics then it would be a big improvement IMO.

First test was putting the modules around the tube .... using Tinkercad I messed around with all the modules trying to fit them in.

Having got them to all fit in a round base I set about figuring out the charging the battery and powering the Nano from the 3.6V battery as the IR receivers were specified to use 5V.

After a good Googling around for some modules I finally found some modules that fit the bill, one to convert 3.6V to 5V and another to charge a single lithium cell from 5V.  These module need to be pretty small and I wanted them to be on a single PCB to make wiring up the modules easy so I designed a PCB to mount them on and had the idea to attach the PCB to the switch which would be securely screwed in to the base.
Power PCB Circuit

Design layout
Final PCB
The outcome for this design means that when switched on the 3.6V battery is connected to the DC/DC converter supplying 5V to the Nano, BT module and the IR beams, when switched off the battery changes to the output of the single cell charger module, which gets it's 5V supply from the nano USB connector therefore charging the battery.  Also all the supply connections for the modules are also on the PCB making it easier to wire up when assembling.

Some More Images


Things you'll need
 Item Link  Cost 
 Pololu 5V Step-Up Voltage Regulator U3V12F5 Link  £3.32
 DD08CRMA Mini 5V 1A Lithium LiPo Charger Module eBay Link  £1.97
 Mini Miniature On/On 6 Pin Slide Switch DPDT eBay Search Link  ~£0.40 ea.
 Power PCB gerber files Link  £0.00
3D Print files for carrier and tube Link £0.00

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