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The Learning Circuit 88: Infinity Mirror Beating Heart with Thermistors

element14 presents
Infinity Mirror Beating Heart with Thermistors

The Learning Circuit | element14 presents |  Project Videos

 

 

In this episode of the Learning Circuit, Karen opens up her heart to us. Literally. Karen shows a fun new way to use a thermistor in a project. Using a thermistor as a variable resistor in an astable 555 timer circuit, Karen is able to create a visual “heartbeat” that changes speed in response to temperature changes. Check out this cool infinity mirror LED project and how Karen shows yet again, that fun and interesting projects can be made with a few simple, and affordable components.

 

Bill of Material:

 

Product NameManufacturerQuantityBuy KitBuy Kit
Prototype Board, Phenolic, 1.6 mm, 45 mm, 91 mm, (2) smallMulticomp1Buy NowBuy Now
NE555PNE555P - Single Precision Timer in DIP-8 Package, 500kHz, 4.5V - 16VTEXAS INSTRUMENTS1Buy NowBuy Now
Thermistor, NTC, 100 kohm, NTCLE Series, 4190 K, -40 °C to 125 °C, Through Hole, Radial LeadedVishay1Buy NowBuy Now
Through Hole Resistor, 100 kohm, 500 mW, ± 2%, Axial Leaded, 250 VVishay1Buy NowBuy Now
Ceramic Disc Capacitor, 0.01 µF, 100 V, ± 20%, 5 mmVishay1Buy NowBuy Now
Electrolytic Capacitor, Miniature, 4.7 µF, 50 V, 515D Series, ± 20%, Radial LeadedVishay1Buy NowBuy Now
AA BatteriesPro Elec3Buy NowBuy Now

 

Additional Parts:

 

Product Name

4.5VDC Heart with built-in LEDs, battery pack, and power switch.

Anonymous

  • An alternative design might be to turn it into a wand. Replace the base with a tube to hold the batteries in-line and then fit a photoplethysmography (did I spell that right ? ) sensor into the handle to measure the actual heart beat of the person holding the wand, and flash the LEDs in time to that.

     

    The thermistor perhaps could be used to change the colour of LEDs as the handle warmed up to body temperature.

  • in reply to miles90

    Yes, from what I read while researching the topic, one of the main applications for thermistors in electronics is to control a cooling system to prevent overheating.

  • Thank you Karen.

     

    Interesting problematic. RC has the dimension of time. For instance a 1uF capacitor associated with a one megohm resistor is a 1s timing RC network. Also, rather than choosing the capacitance, you could use a potentiometer to set the timing value accurately. Using a quartz crystal along with a counter is also a nice way to measure time.

     

    I was thinking of an interesting application of a thermistor. If you have a circuit that is subject to heating (for instance because of high power consumption) than you could use a thermistor to trigger a fan when a higher threshold temperature is reached and stop that fan when a lower threshold temperature is reached. I think PC fans may work that way.

     

    Thanks again Karen.