Cup with heat awareness

[OrangeArav]

Hello guys we need help building a cup that would notify drinkers of hot beverages of the temperature via LEDs. Namely, if the liquid is hot - red light, warm - yellow light, cold - green. The trouble is how to power the circuit. We are not allowed to use lithium-ion batteries, only Ni-Mh; therefore, what we were thinking was to get a wireless USB transmitter for the outside and then use a receiver on the inside. The problem is with the rechargeable batteries... We bought one of the USB charging adapters and want to somehow connect the wireless receiver to the USB adapter and from that to microcontroller to power LEDs. How should we do this? How should we connect the USB adapter to the receiver so that it can charge the batteries once the cup is on the transmitter? This is for a school project so the easiest and fastest way is preferred.

 

[Arouse1973]

Hello. Do you have any information and pictures of the devices you intend to use. If you do then please post them here.
Thanks
Adam

 

[OrangeArav]

Hello. Do you have any information and pictures of the devices you intend to use. If you do then please post them here.
Thanks
Adam

Yes, here's the USB transmitter -
http://www.ebay.com/itm/QI-Wireless...hash=item19f165935d:m:mJbPtsuazPh8BEsZ27jC1XA
USB adapter - http://www.amazon.com/gp/product/B0054LBRJI?psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00
Wireless receiver - http://www.ebay.com/itm/Universal-Q...hash=item419d654b6d:m:mQVEnDfsQG8dNBdf-O_FTWw
Now, we just need to charge the rechargeable batteries from the wireless transmitter/receiver combination. I.e. how to connect the adapter with the rechargeable batteries to power?

 

[Arouse1973]

I think you are going to have to get an adaptor lead which has the mating connector (micro USB I think) and then use a constant current charging circuit for the NiMHs. What is the capacity of the batteries you plan to use? Edit: you might be able to get a cable that connect from the wireless charger to the USB charger.

 

[Arouse1973]

Something like this? http://www.dhgate.com/product/wholesale-lot-20pcs-usb-type-a-female-to/151843394.html

 

[OrangeArav]

Something like this? http://www.dhgate.com/product/wholesale-lot-20pcs-usb-type-a-female-to/151843394.html

These are the rechargeable batteries we're using:
http://www.amazon.com/gp/product/B00JHKSMJK?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
Would it be cumbersome to take apart the USB adapter and grab leads connecting from the wireless receiver to adapter? Also, what is the constant current charging circuit that you mentioned?
The objective is again to have the cup stand on the wireless transmitter disk http://www.ebay.com/itm/QI-Wireless...:m:mJbPtsuazPh8BEsZ27jC1XA&afsrc=1&rmvSB=true (attached to USB) and charge the batteries, when the user picks the cup up, the power to the ckt comes from the batteries. Does it seem reasonable?

 

[Gryd3]

Well... knowing additional details will help.
Will you be using a couple small surface mount LEDs, or a number of larger high power LEDs?
What kind of battery life do you want/need?
Will the LEDs be on all the time?

You could take a look at those cheap garden solar lights. You don't need a very complex charger... something super simple will do.

 

[hevans1944]

Many years ago you could purchase liquid crystal thermometers that consisted of a row of liquid crystal dots, each dot changing color over a narrow temperature range. I still have several of these that work over ambient temperature ranges, but I am pretty sure they can be made to cover the hot, medium, and cold range of a cup of consumable liquid. Sometimes electronics is not the best solution. And too bad McDonald's didn't know about them either.

 

[Arouse1973]

These are the rechargeable batteries we're using:
http://www.amazon.com/gp/product/B00JHKSMJK?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
Would it be cumbersome to take apart the USB adapter and grab leads connecting from the wireless receiver to adapter? Also, what is the constant current charging circuit that you mentioned?
The objective is again to have the cup stand on the wireless transmitter disk http://www.ebay.com/itm/QI-Wireless...:m:mJbPtsuazPh8BEsZ27jC1XA&afsrc=1&rmvSB=true (attached to USB) and charge the batteries, when the user picks the cup up, the power to the ckt comes from the batteries. Does it seem reasonable?

You might not need the constant current circuit I mentioned if you use the USB charger you posted. The constant current charger is in my opinion the safest way to charge NiMh. If you set the current to C/10 you can virtually leave them connected all the time. This does have a disadvantage of taking a lot longer to charge, but in some cases it doesn't matter.
Thanks
Adam