Hi all,

Working on a project that detects EMG data from the forearm and ultimately it will be battery powered. For the meantime I don't really want to run through a wack of batteries as it is quite costly.

Safety is the utmost concern as I will be connecting this to my arm. The commercial isolation transformers online seem to be pretty pricey, wondering if there is a more economical approach to design a system that I can use for prototyping.

It will need to be a 5V supply for some low power op amps/instrumentation amp.

Cheers!

 

It will need to be a 5V supply for some low power op amps/instrumentation amp.

The current draw of these is normally very low, so a battery seems like a very viable option. A 4-pack of AAs could likely be used directly without any regulation circuitry.

 

This doesn't seem like a problem to me. Try a wall wart. Most of us have a box full. Don't you? If not, go to the local flea market and buy a box full of orphaned wall warts for $1 each.

 

Check out DC-DC converters, too. This page from Mouser has bunches of them. There is a standard for medical isolation. Offhand, I can't remember what it is but you might want to investigate that as well.

Have fun.

 

Strictly speaking, what you need is a medical approved power supply. But well as long as you do not connect this equipment to any real patients. Just use any 5 volt power supply. You are working far away from heart. So the hazard real low in your case

 

Just get some rechargeable batteries and swap them as needed. You can get four packs of AA NI-MH really cheap at Fry's. They are good for about 2500 mA-hr.

 

Thank you for the recommendations all.

Think I might just go with the wall-wart.

Cheers.

 

You can do your own evaluation of the safety isolation of a wall wart power supply. There is an AAMI standard for testing that includes the test device, techniques, and safety standards: http://courses.engr.illinois.edu/ece445/documents/Safe_Current_Limits.pdf
The leakage load I've used is in the attached schematic. All you will need to do is attach one lead to an earth ground, and touch the other to your power supply's output leads, one at a time (while it's plugged into the wall). For you patient-connected device, you want a measured reading of less that 50mVAC (50uA).

Ken