Low Cost Analog to Digital Converter Plans

MTM Scientific, Inc.

Collecting and storing experimental data is a common challenge for hobbyists. A popular approach is to use a device for converting analog data into digital data and storing the information on a computer. These devices are called A/D converters: an abbreviation for analog to digital. There is a wide variation in prices for A/D converters and most are expensive. Since hobbyists are usually on a limited budget, we describe here a simple and low cost method to build a basic A/D converter using a single off-the-shelf IC.

This simple circuit for building an A/D converter uses a PICAXE-08M chip. The PICAXE chip is a microcontroller with numerous useful features, including a 10 bit analog to digital converter. The PICAXE chip also has a serial communication feature which can transmit data directly into a PC's serial port. With only 4 lines of simple computer code  (shown below) the microcontroller can be programmed to perform continuous analog to digital conversions and transmit the numerical result once per second. The nonvolatile memory of the PICAXE chip allows the program to be stored indefinitely, and it will recommence whenever 5VDC power is applied.

Note that this circuit is intended for connection directly to the serial port of a standard PC computer. The circuit diagram shows the serial port connections as you view the connector on the computer. The only additional items required are two resistors and a 5VDC power supply. The 5V supply is for the IC power and it also forms the reference for the analog to digital conversion. As you probably know, 5 VDC is available inside a modern computer... for example at any power connector for adding additional storage drives.

This circuit is great with an older PC, in which case you can put together a dedicated data collection system which is also low cost. Most computers include a standard serial port built-in. The data from the PICAXE can be read by any program capable of monitoring a serial port. For example, the HyperTerminal application works well, and it is included free as part of the Windows operating system. A computer running DOS can monitor the serial port by using a shareware version of the old application ProComm ( Such as version 2.4.3.) Whatever serial communication program you use, it is important to have the communication settings correct: 2400 baud, no parity, 8 data bits and 1 stop bit. Each data sample appears as a new line in the scrolling output.  Here is a view of HyperTerminal collecting the data.

The PICAXE chips are available from fellow hobbyist Phil Anderson at his website. He also provides a wealth of additional information for using the chips, including a link to the free software for programming them. The PICAXE chips are programmed using a PC serial port and the same circuit we show here for the A/D converter. By downloading, installing and running the free software you can program a blank chip with the code for this project. The programming software also includes a simple serial port monitor for viewing the data as it is received.

The data collected by the PICAXE chip is converted with a 10 bit accuracy, equal to 1024 digital steps. The reference for the conversion is the 5 volt DC supply. The resolution of the conversion is therefore 5.0 V / 1024 = 0.00488 volts. The smallest observable signal change you can measure is therefore about 5 mV.

There are multiple options you can explore with this same project. For example the PICAXE chip contains 2 additional A/D converters which can be used to increase your data channels. It is also a simple matter to change the frequency of the data collection. Another possibility is modifying the PICAXE code to convert your data into the units of measure (on the chip) before transmitting the data via the serial port.

This simple project makes it very easy to turn even the oldest computer into a useful data acquisition system.

Purchase a PICAXE Chip already programmed for the A/D project...

Some of our customers may wish to purchase a programmed PICAXE chip which is ready to use for this project... in order to get your data collection up and running fast. We are offering a single PICAXE chip, programmed and ready to use, shipped to anywhere in the world, for $10.00

Please note that this offer is only for one programmed PICAXE chip, which provides one channel of 10 bit A/D as shown.  You must supply the other components for this Analog to Digital converter project.

PROGRAMMED PICAXE A/D Chip (Catalog #PICAXE)...$10.00, Worldwide Shipping Included!

BY PAYPAL: click the "PAYPAL, Buy Now" button.  Mail Orders: see details below.

We keep ordering simple!  Prompt, courteous 30 day refund policy.

BY MAIL....please send a Check or Money Order for $10.00 for a programmed PICAXE chip to:

MTM Scientific, Inc.  P.O. Box 522, Clinton, Michigan 49236 USA

There are no shipping delays for Personal Checks.  We make every effort to ship promptly.

BY PAYPAL... Click the "Buy Now" button above, or send a Paypal directly to: mtm@mtmscientific.com and noting the catalog number.

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