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By MARK ROBERTS This easy-to-build I/O card plugs into the parallel port of your PC. It features 11 analog inputs for sampling, plus two analog outputs and eight digital outputs. It’s software con­trolled and can automatically log sampled data on the analog input channels to an Excel spreadsheet. Simple I/O card with automatic data logging T HIS SIMPLE I/O CARD can be used to sample incoming data on up to 11 channels and/or used to control other equipment via its 10 output lines. You can either switch equipment on or off via the digital output lines, or control equipment using a variable 0-5V DC signal from two separate analog outputs. An on-screen “virtual” instrument panel is used to drive the card – see Fig.1. This display is software generated and its functions are easy to follow. On the righthand side of the panel are 10 analog input channels (Channels 1-5 and Channels 6-10), with each channel showing the voltage applied to it. The 11th analog input channel is directly below Channels 1-5 and is labelled “Battery Voltage”. The latter can typically be used to monitor the voltage from a real battery or simply used as an extra input channel. 22  Silicon Chip At the top left of the panel are eight buttons labelled D0-D7. These are used to turn the digital I/O lines on or off. Only one output from D0-D3 can be on at the same time, while any combination of buttons from D4-D7 Main Features •  11 analog input channels (020V) •  2 analog output channels (0-5V nominal – see text) •  8 digital output channels (open collector) •  Analog inputs can be sampled and automatically logged to an Excel spreadsheet •  Logging interval can be set to 10 seconds, 1 minute, 10 minutes or 60 minutes can be turned on at once. When an output is turned on, the indicator light below its button “lights” up. Red indicators are used for outputs D0-D3, while yellow indicators are used for D4-D7. Fig.1 shows how the panel appears with outputs D1, D4, D5 and D7 turned on. It also shows that voltages of 6.45V, 6.36V and 7.82V have been applied to input channels 3, 7 and 9 respective­ly, while a voltage of 6.27V has been applied to the 11th (Battery Voltage) input. Immediately below the digital output buttons are two large analog voltmeters. These show the voltage on each of the two analog outputs. You can easily vary these outputs over the range 0-5V DC by dragging the two slider controls (note: the maximum output voltage depends on the supply voltage from the parallel port). parallel port. The converted digital data is then clocked out from the DOUT pin (pin 16) and applied to pin 13 of the port. The clock signal comes from pin 6 of the parallel port and is applied to pin 18 of IC4 (I/O-CK). This clock signal is also applied to the SCLK (pin 2) inputs of ICs 5 & 6 and to the SRCLK input of IC2. ICs 5 & 6 are MAX515 10-bit A/D converters and these are used to provide the two 0-5V (nominal) analog outputs. As shown in Fig.3, their data inputs (DIN) are tied together and the data clocked in via pin 5 of the parallel port. Pins 7 and 8 of the parallel port control the CS (chip select) inputs (pin 3) of ICs 5 & 6, so that only IC is active at any given time. The MAX515 is programmed by Fig.1: the I/O card is controlled using this virtual instrument panel which is writing 16 bits of serial data, clocked generated by the software. It shows the voltages present on the analog inputs in the following order: four dummy and lets you control the analog and digital output channels. bits, 10 data bits and two sub-LSB zeros. The data is clocked in on the The only other feature of real note tors and the sampled signals are then SCLK rising edge while the CS signal on the main panel is the “Logging” applied to the A0-A10 inputs of IC4 on pin 3 is low and held in a 16function (in the top lefthand corner). for A/D conversion. bit serial register. This data is then Clicking this function brings up the The signal on pin 17 (Address) of transferred to the DAC register when dialog box shown in Fig.5, so that IC4 (applied from pin 3 of the parallel CS goes high to update the output you can automatically log sampled port) selects the input voltage to be voltage. data into an Excel spreadsheet. Of converted. The EOC (end of converThe maximum output from each course, you must have Excel on your sion) output at pin 19 then goes low MAX515 is Vcc-0.4V (Vcc is the voltcomputer in order to do this. when conversion is completed and age from the parallel port). This means Once the data has been logged in, this signals the PC via pin 10 of the that if the computer supplies 5V, then you can then use Excel to produce the maximum analog output will graphs or charts in the usual manner. be 4.6V. REF1, an LM385-2.5Z You can sample the incoming data voltage reference diode, supplies (0-20V) on the 11 analog inputs at a 2.5V reference to the REFIN 10-second, 1-minute, 10-minute or (pin 6) input of both ICs, giving 60-minute intervals just by clicking a resolution of about 2.5mV for the appro­ priate button. We’ll have the two analog outputs. more to say about logging to an Excel Note that the MAX515 DACs spreadsheet a little later on. will not operate if the voltage from the parallel port is down How it works around 3V – see panel. Now take a look at the circuit – see ICs 2 & 3 provide the digital Fig.3. The circuit uses six ICs plus a outputs. IC2 is a 74HC595 8-bit 2.5V voltage reference and not much serial in/parallel out shift regiselse. ter. The data comes in on pin 14 The four main ICs in the line-up (SER) and is clocked into a D-type are a 74HC595 shift reg­ ister (IC2), storage register when RCLK (pin an MC145041 8-bit A/D converter 12) goes high. The data on the E (IC4) and two MAX515 10-bit D/A (enabled) pin deter­mines which converters (IC5 & IC6). Each of these register is being updated. main blocks is controlled via a 3-wire The eight outputs from shift serial interface that’s compatible with register IC2 directly drive IC3 SPI, QSPI and Microwire standards. which is a ULN2803 Darlington IC4 is used to sample and digitTransistor Array. This device has ise the data on the 11 analog input Fig.2: this block diagram shows the main open collec­tor outputs and these channels (Ch1-Ch10 and Batt). Each circuit sections of the I/O Card. The card can be used to drive LEDs, relays input signal is fed to a voltage divider is controlled using software, with signals or opto-couplers, to control other consisting of 330kΩ and 39kΩ resis- sent via the PC’s parallel port. circuits. The maximum voltage August 1998  23 Fig.3: the circuit uses six ICs, with each of the main blocks controlled via a 3-wire serial interface. IC4 performs A/D conversion for the analog inputs, while D/A converters ICs 5 & 6 provide the two analog outputs. ICs 2 & 3 provide the eight open-collector digital outputs which can be used to drive relays or LEDs. that can be switched by the open collector outputs is 30V. IC1 doesn’t really play any role in the circuit operation as such. This device is a Dallas Semiconductor DS­ 24  Silicon Chip 2401 Silicon Serial Number. It comes in a standard TO-92 package but only two of its pins (Data and GND) are used. Each of these devic­es comes with a unique registration number and this number is read by the software via pin 15 of the parallel port. If the number matches the number programmed into the software, the software functions normally. If they don’t match, a demon­stration version of the software is loaded instead. This means that the software supplied with each individual DS2401 Fig.4: follow this parts layout diagram to assemble the PC board. As shown here, IC3 is driving eight LEDs but you can easily modify the circuit to drive relays or opto­couplers. is tailored to match that device. The same software will not work with other hardware because the code number will be different. Power for the circuit is derived from pin 9 of the parallel port which supplies a +5V rail. This means that no external power supply is required. Construction All the parts, including the DB25M connector, are installed on a small PC board measuring 76 x 68mm. Fig.4 shows the assembly details. Begin the assembly by installing PC stakes at the external wiring positions (ie, at the analog inputs, at the outputs and at the GND positions). This done, install the 10 wire links, noting that three of these links (shown dotted) are under ICs 2, 5 & 6. The resistors and the capacitors can go in next. Take care to ensure that the two 100µF electrolytics are installed with the correct polarity. Note that our prototype shows the eight digital outputs driving eight LEDs via 2.2kΩ resistors. This is also shown on the layout diagram (Fig.4). If you want to drive relays or optocou­ plers, the output circuit should be modified accordingly. For example, a relay can be driven by connecting it directly to an output of IC3 as shown on Fig.3. The six ICs (including the DS2401) can go in next, followed by the LM385 2.5V voltage reference diode. Note that the DS2401 and the reference diode both look the same, so be careful not to get them mixed up. Finally, complete the assembly by installing the DB25M connector. Check that this part lies flat against the PC board before soldering its pins. Go over your work and check the PC board carefully for mistakes before connecting the unit to a computer, ready for testing. You can either plug the unit direct­ly into the parallel port or connect it via a DB25 male-tofemale cable. Installing the software The software comes on two floppy discs and runs under Wind­ows 3.1x, Windows 95 and Windows NT. You install it by running setup.exe on the first disc and then following a few onscreen instructions. In Windows 95, for example, you click Start, Run and then type A:\setup.exe in the space provided (assuming that the floppy No Analog Output? The MAX515 10-bit D/A converters specified will not work if the voltage from the parallel port is down around 3V. If that happens, there will be no voltage on the analog outputs, regard­less of the slider settings. There are two ways around this problem: (1) Use the optional LPT2 card from Softmark (this card supplies about 4.95V); or (2) Use an external 5V DC power supply to power the circuit. If you choose this option, remove link LK2 and connect the external +5V rail to the vacant pad next to IC2. disc is in the A: drive). The installer program creates the appropriate program group and installs a shortcut in the Start menu. In Windows 3.1x, you click File, Run and type A:\setup.exe. When you boot the software, it first opens a dialog box that lets you select between two printer ports (LPT1 and LPT2). LPT2 is the initial default but most users will need to select LPT1 since they will only have one parallel port on their comput­er. You then click OK to bring up the instrument panel shown in Fig.1. Initially, all the displays will be off, since the Power is off. You turn the display on by clicking the Power button. Parts List 1 PC board, 76 x 68mm 1 PC-mount DB25M connector 1 2-disc software package 4 PC stakes Semiconductors 1 DS2401 silicon serial number (IC1) 1 74HC595 8-bit shift register (IC2) 1 ULN2803 Darlington transistor array (IC3) 1 MC145041 8-bit A/D converter (IC4) 2 MAX515 10-bit D/A converters (IC5 & IC6) 1 LM385-2.5Z 2.5V reference (REF1) Capacitors 2 100µF 16VW PC electrolytics 2 0.1µF monolithic Resistors (0.25W, 1%) 11 330kΩ 9 2.2kΩ (see text) 11 39kΩ 1 120Ω By the way, once you’ve selected a port, it can be saved as the default by clicking the Power button to off (this rewrites the io.ini file). The software will now always boot with the new port as the default, unless you change it again. Testing It’s now just a matter of checking that everything works. To do this, first August 1998  25 Fig.5: clicking “Logging” on the virtual instrument panel brings up the Logging System I/O Interface shown at right. This lets you select the logging interval, after which you can automatically log to an Excel spreadsheet as shown above. connect a voltmeter to each analog output in turn (ie, between the output and GND) and check that the output voltage can be varied from 0-5V (nominal) as you drag the slider under the corresponding meter. The eight digital outputs can now be checked. Each output should initially be high and should go low when its corresponding button is clicked on the instrument panel to turn it on. Note that because the digital outputs are open collector outputs, you will need to connect a load to test them; eg, a relay or a LED in series with a 2.2kΩ resistor. Don’t forget the wire a diode across the relay coil as shown in the circuit, to quench the back EMF generated when the relay turns off. If you don’t do this, you Where To Buy Parts Parts for this design are available from Softmark, PO Box 1609, Hornsby, NSW 2077 (phone/fax 02 9482 1565). Prices are as follows: Hardware MAX515 10-bit D/A converter ..............................................................$8 MC145041 8-bit A/D converter ............................................................$5 ULN2803 transistor array .....................................................................$4 74HC595 8-bit shift register .................................................................$3 LM385-2.5Z reference diode ................................................................$1 DB25M connector ................................................................................$2 PC board ............................................................................................$10 Full kit (hardware only) .......................................................................$40 Optional LPT2 card ............................................................................$15 Software (two discs) plus DS2401 Version 2.0 with logging .....................................................................$32 Version 1.0 without logging ................................................................$22 Payment by cheque or money order only. Please add $5 for postage. Note: the software associated with this design is copyright to Softmark. 26  Silicon Chip can destroy the switching transistors in IC3. If the circuit is working correctly, then either the relay will turn on or a LED will light when its corresponding digital output is clicked on. Now apply a voltage from 0-20V to each of the analog inputs in turn and check that the correct voltage is displayed for each channel. If you have a variable supply, check that the reading varies as you vary the input voltage. To check the logging feature, click Logging at the top left of the main Window. The “I/O Interface - Logging System” dialog box will now open (see Fig.5) and you should be able to start the automatic logging process by selecting the “Logging Interval” and clicking the On button. Excel should now automatically be launched and the sampled data automatically logged into the spreadsheet at the selected time intervals (see Fig.5). To stop the logging process, click the Off button on the Logging System dialog box. The program will then instruct you to click the Save + Exit button, after which you can save the spreadsheet data in Excel to a file and directory of your choosing. The Logging System dialog box can now be closed by clicking the Main Form SC button.