Clock & Timer Circuit DiagramsLCD-LED Display

Thermometer with Four-Digit LED Display Schematic Circuit Diagram

Introduction to Philips SAA1064 LED Driver IC

The Philips SAA1064 LED driver IC has long been an unofficial standard for powering seven-segment LED displays. Capable of driving four-digit displays via an I2C bus, it has been widely used. However, the IC, regardless of packaging (DIL24 or SO24), features a relatively large footprint with its 24 pins. Furthermore, its minimum supply voltage of 5 V and quiescent current of nearly 10 mA are no longer considered state-of-the-art specifications.

Thermometer with Four-Digit LED Display Schematic Circuit Diagram

Introduction: Maxim MAX6958 IC for Digital Thermometer Circuit

An excellent alternative for applications of this nature is the Maxim MAX6958 IC. Unlike its predecessor, it comes in a smaller QSO package with just 16 pins, operates at a lower voltage of 3.3 V, and features a shutdown mode consuming only 20 µA. Encouraged by these advancements, the author decided to create a digital thermometer circuit utilizing this IC. Apart from the MAX6958, the circuit requires four common-cathode LED display modules (Toshiba TLR 324) and an Atmel AT89C2051 microcontroller (other variants could also be used). Additionally, a suitable temperature sensor is needed, and the National Semiconductor LM75 was chosen for its compatibility with the I2C protocol. The microcontroller’s clock signal in this straightforward setup can be generated by any crystal with a frequency ranging from 4 to 12 MHz.

Challenges in Firmware Development and Display Driver Complexity

During the assembly language firmware development, the author encountered challenges due to the complexity of the display driver, arising from the limited number of pins. The specific multiplexing technique utilized by Maxim in this context has been extensively discussed in a previous Elektor publication [1].

In-Depth Understanding and Accessible Resources

For those interested in delving into the inner workings of this driver IC, a comprehensive explanation can be found in Maxim Application Note 1880 [2]. Additionally, the article’s Elektor web page [3] offers not only a precompiled hex file but also the author’s meticulously annotated source code, allowing enthusiasts to modify the software to their preferences. For those preferring a hassle-free approach, pre-programmed microcontrollers can be ordered directly from the Elektor Shop [3].

1] Charlieplexing, Elektor July & August
2006; www.elektor.com/060124
[2] www.maxim-ic.com/app-notes/
index.mvp/id/1880
[3] www.elektor.com/080536

Activation and Functionality Check of LED

Upon successful setup, the LED in close proximity to the processor will initiate a blinking pattern at a frequency of 1 Hz. If you have reached this stage without encountering any issues—which, frankly, there seems to be no reason why you wouldn’t—then your system is operational. At this point, you are ready to commence developing your own applications tailored to your needs and interests. If you happen to conceive an intriguing project, we encourage you to share it with us. Don’t hesitate to send your creation our way; we are eager to assess it and potentially feature it in Elektor. (On a side note, it’s worth mentioning that I, the author of this article, did not manage to secure an LPCXpresso board, despite my involvement in its creation.)

Procuring LPCXpresso Board

For those of you who haven’t obtained the complimentary LPCXpresso board, there’s no need to worry. You can purchase one from numerous leading component suppliers or directly from the source [2]. Feel free to acquire this valuable resource to enhance your electronics projects and experiments.

Internet Links
[1] http://ics.nxp.com/lpcxpresso/
[2] www.embeddedartists.com/products/
lpcxpresso/
[3] http://lpcxpresso.code-red-tech.com/
LPCXpresso/Home
[4] http://elektorembedded.blogspot.com

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