The LPT tester

If you are a novice programmer, you want to program applications that offer feedback and are quantifiable. You need to know that your software does what you expect it to do. For these people I have built (many moons ago) a circuit that will do just that. It's a toy, but it will learn you how to write software for the toy and learn about speed implications of your programming language and style.

If you are interested, download LPTester.Zip now. In the ZIP file are:

LpTester.SCH
PADS LOGIC file for schematic drawing
LpTester.LPR
LaserPRinter ready printout of the circuit
LpTester.MPR
Dot MatrixPRinter ready schematic drawing
LpTester.ASC
NetList for PADS PCB of this circuit

If you want hardcopy on a laserjet enter this command:

Copy lptester.LPR PRN

If you prefer a dot matrix printer, enter the command:

Copy lptester.MPR PRN

Or import the file LpTester.SCH into your PADSDEMO software (available from this site) and process it as you feel fit.

The LPTESTER is a small circuit that encompasses:

8 LED's that light up when told to do so
8 open collectors for controlling relays and such
1 Analog to digital converter, 8 bits, single channel (upgrade to 10 bits is possible)
1 temperature sensor (NTC) (connect to ADC)
1 light level sensor (BPW-40) (connect to ADC)

The LED's are controlled by a buffer of type ULN 2803. The open collectors of the ULN's are brought to the outside with a connector so that you can control some relays with it, if you want it.

The ADC is a Texas Instruments TLC 549 serial ADC. It is an 8 bit converter with 5 Volts full scale. The converter is controlled with a ChipSelect input and a Serial CLock. On it's output it clocks out the conversion results bit by bit. It's not very fast but if well programmed in a suitable language you can still obtain 50 kSps (kilo-samples per second). Which is not bad at all.
The temperature sensor is an NTC with a resistor connected in series. The lightsensor is a BPW-40 phototransistor with a pull up resistor.

You can build this device (including a TEKO cabinet) for less than EUR 25.
I won't explain how all the circuits work. It would spoil the fun for you. Just build it and try to get the LED's blinking.

If that works, try to get the ADC working. For this to succeed, make sure you have obtained the right datasheets from the TI websites and take care to understand what's being explained. Still, you will run into many "trouble". Strange things will happen, but I promise that it's not the chip that is misbehaving.... It's all in the datasheet....

If the ADC is working, attach the lightsensor to its input and measure the ligth intensity under the following conditions:

in sunlight, high speed and low speed
under a flashligth, high and low speed
near a fire
under a TL lamp, high and low speed
under an incandescent lamp, high and low speed
under a halogen lamp, high and low speed

Try to explain your observations and find applications for what you observed.

Page created around 1996,