{"id":839,"date":"2015-04-10T21:19:53","date_gmt":"2015-04-10T21:19:53","guid":{"rendered":"http:\/\/blogs.discovery.wisc.edu\/projects\/?p=839"},"modified":"2015-04-20T01:38:15","modified_gmt":"2015-04-20T01:38:15","slug":"4102015","status":"publish","type":"post","link":"https:\/\/blogs.discovery.wisc.edu\/projects\/2015\/04\/10\/4102015\/","title":{"rendered":"4\/10\/2015 TEB Update"},"content":{"rendered":"

There is quite a lot of progress that has happened since my last post, but I’m going to start with the most significant breakthrough I had. \u00a0I found the source of all my problems and it stemmed from my lack of understanding of the difference between N-channel and P-channel MOSFETs. I understood that P-channel MOSFETs were used to switch HIGH side voltages, but I did not understand that the logic was the inverse to N-ch MOSFETs! What this means is that I did not know that in order to close P-ch MOSFETs, you need to pull the Gate voltage LOW. I’ve used N-ch MOSFETs in my day so, intuitively, I \u00a0thought P-ch was turned on the same way as N-ch; pull the Gate HIGH. \u00a0Boy, was I wrong. So now onto what this means for my application. I have the gates of my N-ch and P-ch MOSFETs connected (HeatPulse and ColdPulse) so when HeatPulse is set to HIGH, there is a direct short to GND because the other P-ch remains closed since the gate is being pulled LOW by a pulldown resistor. This is shown below<\/p>\n

\"H-Bridge<\/a><\/p>\n

There are a few solutions to this. One would be to implement an inverter between the MCU and the P-ch MOSFETs to invert the signal. The better solution I see though to purchase an H-bridge IC. This would eliminate many problems.<\/p>\n

I also tested the thermoelectric module at different Power values to see how pronounced the temperature differential was. It turns ou that @3.8v and 800ma, the temp gradient is more than substantial for this application. This means I can remove the voltage boosting circuitry for the next iteration of the PCB. Currently, I have bridged the batttery voltage directly to the source of the transistors.<\/p>\n

And then also for the next iteration, I’m looking to change the form factor of the PCB so that it is integrated\u00a0into the wrist strap. Right now, it’s too bulky and cumbersome so I plan make it thinner as well.<\/div>\n

 <\/p>\n

Next Week’s Work<\/strong><\/p>\n

For the symposium, I plan to just present the cooling feature with the\u00a0voltage supplied either from a transformer connected to a wall outlet or the Lithium Ion battery. I need to remove the P-channel transistor and connected the voltage input of the thermoelectric module directly to Vsource. I need to consolidate the PCB, TE Module, heatsink, wrist strap, and battery into a single unit. Then I’ll play around with timing to get the optimal frequency of sending pulses.<\/p>\n","protected":false},"excerpt":{"rendered":"

There is quite a lot of progress that has happened since my last post, but I’m going to start with the most significant breakthrough I had. \u00a0I found the source of all my problems and it stemmed from my lack … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":101,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[33],"tags":[],"_links":{"self":[{"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/posts\/839"}],"collection":[{"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/users\/101"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/comments?post=839"}],"version-history":[{"count":4,"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/posts\/839\/revisions"}],"predecessor-version":[{"id":849,"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/posts\/839\/revisions\/849"}],"wp:attachment":[{"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/media?parent=839"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/categories?post=839"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.discovery.wisc.edu\/projects\/wp-json\/wp\/v2\/tags?post=839"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}