Voltage regulator problem

[bdg]

Hi Steve,
could you explain this a little further? "A really simple option is to use one of these in series with your heating element and bonded to it so that it cycles on and off around the temperature you want:" I used two 9V in series but the output was like 5V. Do you mean something different? and what does 'bonded to it mean?'

Thanks
Brian

 

[CDRIVE]

And what power source do you intend to use? You probably wouldn't want to use less than 6 AA cells. In fact there is a reasonable argument that you should use larger batteries.

A really simple option is to use one of these in series with your heating element and bonded to it so that it cycles on and off around the temperature you want:

Something like this

Note that that one is 160C, way hotter than you want. I'm sure they're made in lower temperature ratings.

Hi Steve,
could you explain this a little further? I used two 9V in series but the output was like 5V. Do you mean something different? and what does 'bonded to it mean?'

Thanks
Brian

Forget the 9V batteries, they're not suitable! Steve is describing a simple circuit that's comprised of only 3 elements... Battery, Thermostat and heater wired in series. The thermostat is a two terminal device (see Steve's link) that is basically a switch. The contacts open when its rated temperature is reached and closes again when the temperature falls below its rated temperature. It needs to be physically bonded to your heater. In other words when your heater reaches 'n' deg. the thermostat will be the same temperature.

Chris

 

[bdg]

Thanks Chris, I am on it

 

[CDRIVE]

I should point out that the thermostat need only be bonded to the concoction that you described earlier. The important thing is that it sense the same temperature that the patient does.

Chris

 

[bdg]

Thanks Chris,
Steve's link appears to be a company in Australia. Do you have any suggestions on where to get one locally or on the web?

 

[(*steve*)]

RS is world-wide. Alternatively look at the technical documentation, find the manufacturers part number (RS seem to hide this), and search for it on other sites.

Knowing where you are (place it in the location field of your profile) can help us help you in respect of finding suppliers.

 

[CDRIVE]

This Model equates to 122 deg. F. but I've had further thoughts on this design. While it's simple it has two drawbacks that you may not be able to live with. The first is it's large and bulky. The second is it's not adjustable in any way.

It would be more complex but I think you would be well advised to have an adjustable temperature design. This could be accomplished using a Thermistor or solid state sensor. This would require 4 conductors maximum connected to the heat patty. If the Thermistor/Sensor is committed to V- or V+ it could be done with only 3 conductors.

Steve, bdg lives about 70 miles south of me in Miami. Miami is a commerce hub to Central and South America. The Caribbean too. He should have a plethora of suppliers and PCB manufacturers.

Chris

 

[bdg]

Thanks Steve & Chris,

Since using a Termistor or solid state sensor is more complex, what would be the next steps in designing the PCB?

 

[CDRIVE]

Thanks Steve & Chris,

Since using a Termistor or solid state sensor is more complex, what would be the next steps in designing the PCB?

Talk about putting the cart before the horse! It isn't done that way. Below you will find the typical / basic steps (SOP) for circuit design and implementation.

(1) Operational Concepts are discussed and agreed upon with design engineer.
(2) Engineer designs and draws schematic based on (1).
(3) Engineer breadboards or prototypes number (2). This step may or may not include PCB design.
(4) Engineer bench tests the breadboard / prototype and records the resultant data under varying conditions that could be expected in the field..
(5) Engineer converts schematic to a PCB design layout.
(6) A first generation or prototype board is made.
(7) Engineer bench tests and field tests the PCB prototype.
(8) An enclosure is designed.
(9) The device is housed in the enclosure and tested again.

After the above is done then comes the approval from electrical, electronics and safety agencies. In your case you will also have to deal with agencies governing and regulating BIO-MED electronics.

All that said, the circuit will not be overly complex.

Chris