Prop using an ADC as EKG

Comments

• borisg Posts: 39

  2013-03-11 03:00 edited 2013-03-11 03:00

  A lot more sophisticated circuit than I used for my first EKG amplifier 33 years ago. EKG is easy to pick up and the main thing one needs is good CMRR in whatever circuit one builds (3 electrodes are a must if one wants to reject 60 Hz interference without a 60 Hz notch filter). OTOH, one can just buy an EKG amplifier:
  https://www.olimex.com/Products/Duino/Shields/SHIELD-EKG-EMG/
  Have ordered a couple of them and will post my experiences with it once I have a chance to try them out. Goes for about 20 euros (presumably around $28 US as they were $28 CAD from a Canadian distributor). Uses limb leads with ground lead being leg. My preference is for chest leads and third lead can go anywhere that have close resistance between the two chest leads.
• Peter KG6LSE Posts: 1,383

  2013-03-11 19:24 edited 2013-03-11 19:24

  Use of the optocoupled data output inherently increases the risk of shock

  . Umm Is it not the other way around ?,,,,, My Real ECG / Defib ( Lifepak 10 uses loads of Opto Isolators most isolators will do 7.5 kV .
  
  I wish I had more time to play with this as I know my unit is Very accurate for what it is and would make a Great CAL source
  
  Peter..
• Rayman Posts: 13,860

  2013-03-14 03:53 edited 2013-03-14 03:53

  I did PropEKG a long time ago, but was just taking a look at what I did back then...
  Want to do a similar thing now, but this time for a strain guage...
  
  It's not just Prop ADC though, there's an instrument amplifier on the front end.
  The instrument amplifier circuit was the hard part...
  
  Vaguely remember that I was limited in choices because I wanted to use through-hole and not smt.
  I think I couldn't find a single supply version in through-hole.
  
  But, this time I'm more comfortable with SMT, so I think I'll try to find a single supply version that can do the same thing.
  This will make the circuit a lot simpler.
  May still use the Prop for final ADC, have to think about that...
  
  Update: Actually, looking around I think I found a single supply one in DIP too...
  
  Actually, forget my earlier comments (it's been a long time!)... I found the circuit and I was using it as single supply...
  It was an AD627 instrument amp with a 100Meg resistor setting the gain followed by two OPA2107 amps. One was to maintain a reference level and the other to boost the output 100X bigger.
• frank freedman Posts: 1,975

  2013-03-14 20:35 edited 2013-03-14 20:35

  Correct, isolation is standard, no exceptions I have seen. From isolated inputs to isolated low power supplies. Opto or magnetic isolation is used to keep from harming patients. All medical devices coming into our facility must be safety checked as part of the incoming inspection and inventory. Case leakage for example is limited to 600uA. Other more strict limits apply depending on function and area of use. One of the ultrasound machines I work on, uses a small high frequency toroidal transformer (about 1" in diameter) to supply the input circuits.
  
  

  Peter KG6LSE wrote: »

  . Umm Is it not the other way around ?,,,,, My Real ECG / Defib ( Lifepak 10 uses loads of Opto Isolators most isolators will do 7.5 kV .
  
  I wish I had more time to play with this as I know my unit is Very accurate for what it is and would make a Great CAL source
  
  Peter..