In this tutorial i am going to make a simple temperature indicator.The main component of this project is a lm35 temperature sensor.And using a max7219 8*8 led matrix we can indicate the temperature range with emojis in this case i am using 3 different emojis to indicate the temperature range.
For example we can indicate low temperature with smile emoji
Medium temperature with neutral emoji and high temperature with sad emoji.
In this case i am reading my body temperature so that
Smile for temperature <35 div="">
Neutral for temperature between 35-40
Sad for temperature >40
So lets start project
Lm35
Features
• Calibrated Directly in Celsius (Centigrade)
• Linear + 10-mV/°C Scale Factor
• 0.5°C Ensured Accuracy (at 25°C)
• Rated for Full −55°C to 150°C Range
• Suitable for Remote Applications
• Low-Cost Due to Wafer-Level Trimming
• Operates From 4 V to 30 V
• Less Than 60-μA Current Drain
• Low Self-Heating, 0.08°C in Still Air
• Non-Linearity Only ±¼°C Typical
• Low-Impedance Output, 0.1 Ω for 1-mA Load
Description
The LM35 series are precision integrated-circuit temperature devices with an output voltage linearly proportional to the Centigrade temperature. The LM35 device has an advantage over linear temperature sensors calibrated in Kelvin, as the user is not required to subtract a large constant voltage from the output to obtain convenient Centigrade
scaling. The LM35 device does not require any external calibration or trimming to provide typical accuracies of ±¼°C at room temperature and ±¾°C
over a full −55°C to 150°C temperature range. Lower cost is assured by trimming and calibration at the wafer level.The low-output impedance, linear output, and precise inherent calibration of the LM35 device makes interfacing to readout or control circuitry especially easy. The device is used with single power supplies, or with plus and minus supplies. As the
LM35 device draws only 60 μA from the supply, it has very low self-heating of less than 0.1°C in still air. The LM35 device is rated to operate over a −55°C to 150°C temperature range, while the LM35C device is rated for a −40°C to 110°C range (−10° with improved accuracy). The LM35-series devices are
available packaged in hermetic TO transistor packages, while the LM35C, LM35CA, and LM35D devices are available in the plastic TO-92 transistor
package. The LM35D device is available in an 8-lead surface-mount small-outline package and a plastic TO-220 package
8*8 led matrix
MAX7219 IC
The MAX7219/MAX7221 are compact, serial input/out-put common-cathode display drivers that interface microprocessors (µPs) to 7-segment numeric LED displays of up to 8 digits, bar-graph displays, or 64 individual LEDs. Included on-chip are a BCD code-B decoder, multiplex scan circuitry, segment and digit
drivers, and an 8×8 static RAM that stores each digit.Only one external resistor is required to set the segment current for all LEDs. The MAX7221 is compatiblewith SPI, QSPI, and MICROWIRE, and has slewrate-limited segment drivers to reduce EMI.
A convenient 4-wire serial interface connects to all common µPs. Individual digits may be addressed and updated without rewriting the entire display.TheMAX7219/MAX7221 also allow the user to select code-B decoding or no-decode for each digit.
The devices include a 150µA lowpower shutdown mode, analog and digital brightness control, a scan limit register that allows the user to display from 1 to 8 digits, and a test mode that forces all LEDs on.
8*8 led matrix
8×8 matrix consists of 64 dots or pixels. There is a LED for each pixel and these LEDs are connected to total of 16 pins.
As you can see all anodes of same row is connected to one pin and all cathodes of same column are connected to another pin.We have 8 row pins and 8 column pins. If a positive voltage is applied to R1 pin and negative to C1, we can see that the first pixel turns on. If we apply negative to C2 then the second pixel turns on. Like this we can turn each pixel by hanging the supply pins. However we have 64 supply combinations, and doing it manually is practically impossible. That is why we use max7219 driver and arduino for interface this matrix
circuit diagram
Leave a comment