A few months ago I acquired a Tektronix 222 oscilloscope, and as expected the SLA battery was completely dead. It also didn't look like there was much in the way of a direct replacement, so I thought it would be a nice challenge to build a module that will allow to use the scope with standard 18650 Li-Ion cells.
Well, here is the result:
It's quite a simple circuit in principle: There is a battery charger to charge the Li-Ion cells, and a boost converter to step up the battery voltage to the 8V required by the scope. When the scope is plugged in, it will output 9.5V on its battery connector to charge the battery. The circuit simply detects this voltage level, and switches between the charger when the scope is plugged in, and the boost converter otherwise. On a high level, it looks like this:
There are obviously a few other little additions like cell protection, and quite a few interesting design trade-offs along the way. Being well aware that this is a shameless plug, I have written up a rather more detailed description on my website (
http://kitsune-denshi.net/projects:tek222bat), where you can also find the schematics, BOM and everything else you might be interested in. Component cost for the circuit was around £20, plus boards and laser cut acrylic for the case. Not too bad in my opinion to make the scope battery powered again.
When doing my initial research, I came across quite a few people who seemed to have similar difficulties with finding replacement batteries - so maybe this module will be of interest to someone else too
If you do want to build your own, I have a bunch of bare boards left over and would be happy to send them out to people. Be aware that some minor bodges are required to get the boards working, though.
Let me know that you think, I'm keen to hear some opinions on this project.
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