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More LEDs, more patterns, more exciting than ever 32-led Flashing LED displays are always intriguing, particularly if they emulate the KnightRider car from the old TV series. This KnightRider light chaser includes 12 different lighting patterns using 32 LEDs for a big and impressive display. Not restricted to KnightRider use, the display can be used as a rear window brake light or as an eye-catching conversation piece at parties or even on retail displays. By JOHN CLARKE 24  Silicon Chip www.siliconchip.com.au I the other in May 1996. Both of these Our latest version of KnightRider n the early 1980s there was a TV used 16 LEDs and had a single fixed has twice as many LEDs, 32, and a series called KnightRider. Its “star” scanning display pattern. number of different display patterns was a rather clever car going by the are available which are selectfetching name ‘Kit’. ed using a pushbutton switch. Mind you, Kit was no There are four scanning seordinary car. It had powers quences, a chaser and a strobe. and abilities far beyond those Ds LE 32 of mortal cars. Kit could talk, If you mounted the display * including medleys s, rn tte pa y pla drive itself and supposedly on your car’s parcel shelf, you dis D LE * 12 d see using a row of lights on could also use it as a brake ee sp rn tte pa * Adjustable the front which ‘scanned’ from light. ss tne igh br side to side to simulate moni* Adjustable LED The patterns toring what was ahead. * 12V operation While the KnightRider TV The four scanning patterns series has long since ceased, include the traditional moveBut both of these were in the days such scanning lights have ment of LEDs from left to right and before microcontrollers – or at least becontinued appeal and we have pubfrom right to left which is repeated fore microcontrollers were commonly lished two different KnightRider light to simulate scanning across a field used in projects. displays, one in November 1988 and in front of the LEDs. Pattern 2 begins Features Fig.1: in this circuit, the 32 LEDs are arranged in an array, driven in their various patterns by the PIC microcontroller. www.siliconchip.com.au May 2002  25 with two LEDs in the centre LEDs which then spread (light up) to the left and right and contract back to the centre. Patterns 3 and 4 are similar, with pattern 3 moving from the centre to the outside and then back to centre again. Pattern 4 starts from the outside LEDs and moves to the centre and then back the outside again. Chaser sequences include a right to left movement and a left to right movement. The strobe patterns can be at a regular or random flashing rate. For brake light use, there are two patterns. The first lights all LEDs initially for a minimum of about 18 seconds (depending on the speed setting) and then the LEDs randomly switch off until they are all out. Alternatively, you can just have all LEDs lit while ever the brake is applied. The KnightRider PC board measures 210 x 72mm. All 32 LEDs mount horizontally along one edge of the PC board. There are two trimpots, one to adjust the LED scanning rate and the other to adjust display brightness. A pushbutton selects the display pattern while a LED next to the switch flashes once or more to indicate the pattern that has been selected. Circuit description Apart from the 33 LEDs, the KnightRider uses relatively few components and is based around IC1, a PIC16F84 microcontroller. This provides all the LED patterns. The PIC16F84 has 18 pins, 13 of which can be used as inputs or outputs. For our circuit we are using 12 as outputs to drive the LEDs and one as an input and an output to monitor the pattern select switch and drive the pattern LED. Fig.1 shows the circuit details. Multiplexed rows and columns While the 32 LEDs are physically arrayed along one side of the PC board, they are actually connected as a matrix of four columns and eight rows, as shown in Fig.1. The eight rows are driven directly from IC1 (RB0-RB7) while the four columns are driven by four transistors, Q1-Q4. These transistors are switched by the RA0, RA1, RA2 and RA3 outputs of IC1. When the RA0 output (pin 17) is pulled low by IC1, transistor Q1 is switched on and applies power to the anodes of LEDs 1-8. A low output on any of the RB outputs will drive the LED connected to it via its series 150Ω resistor. For example, if RB0 goes low, LED1 will light. The RA0 line is kept low for a short time before this goes high to switch off Q1. Thus LEDs1-8 are switched off. The RA3 line (pin 2) is then brought low to drive Q2 and the anodes of LEDs 9-16. Now any low RB outputs will then light up LEDs 9-16. Similarly, RA2 (pin 1) is brought low to drive Q3 and LEDs 17 to 24 and then RA1 (pin 18) is pulled low to drive Q4 and Scope 1: The upper trace is the oscillator waveform at pin 16 (OSC IN). This is a classic sawtooth expected from a relaxation oscillator. The lower trace is the waveform at pin 15 (OSC OUT) which in this RC mode is a square wave at one quarter the oscillation frequency. 26  Silicon Chip LEDs 25-32. This cycle repeats endlessly with each column of eight LEDs being lit at a very fast rate so that the LEDs appear to be continuously lit rather than only being on for some of the time. This system of driving the LEDs is called “multiplexing”. Its big advantage is that it saves power and drastically reduces the number of connections required. If the LEDs were not multi-plexed we would need 33 separate lines (32 actives and one common) whereas with multiplexing we can drive the 32 LEDs using only 12 lines connected in the matrix. Brightness control Overall LED brightness is controlled with trimpot VR2. This varies the voltage at pin 3 of IC2 from 5V down to about 2.4V when the wiper is at its lowest point. Op amp IC2 operates as a unity gain buffer amplifier, with transistor Q5 providing extra current drive capability. If the emitter of Q5 is at 5V, the LEDs will be driven at maximum brightness. Typical LED current will be (5V - 1.8V)/150Ω, or 21mA. This is the pulse current, not average current. The pattern select switch S1 connects to RA4 of IC1. This pin is normally held at 5V via the 10kΩ pullup resistor. When S1 is pressed, LED33 lights and RA4 is pulled low. This is recognised by IC1 as a switch closure and the next pattern in the sequence of 12 is selected. When the Scope 2: These traces show the time duration between when power is applied to the circuit and when the LEDs light for the brake light pattern selections. Top waveform is the applied voltage and when this goes high, there is some 67ms before the LEDs light. This is fast enough to display almost instantly the brakes are applied. www.siliconchip.com.au 15pF DEEPS VR1 50k 0.1F K K 4.7k 150 LED31 150 LED30 150 IC1 PIC16F84 LED29 150 LED28 1 10F 1k A 22k 68k 150 10k 150 NRETTAP Q6 BC328 150 150 LED27 LED26 LED25 LED24 LED23 S1 LED22 LED33 10k LED21 10F Q5 BC338 10F + LED18 LED17 LED16 LED15 THGIRB Q3 BC328 VR2 50k LED14 LED13 Q2 BC328 680 680 LED12 LED11 Q1 BC328 680 LED10 LED9 12050180 Q4 BC328 680 2002 C LED19 10F 1 LED20 47k IC2 LM358 1k LED32 LED8 LED7 REG1 10F LED6 LM7805 +12V +12V LED4 16V ZD1 LED3 10 1N4004 KNIGHT RIDER LED2 D1 LED1 A 0V GND LED5 100F A Fig. 2: here’s the full-size PC board component overlay, with a matching photo to make assembly a breeze! switch is released, IC1 flashes LED33 to indicate the pattern selected. For example, pattern 2 is indicated by two flashes. Note that the RA4 pin is an open drain output when configured as an www.siliconchip.com.au output. This allows RA4 to drive LED33 when pin 3 is low. When RA4 is set high, the open drain connection means that it becomes a high impedance output which is pulled high via the 10kΩ resistor. In this condition, IC1 can monitor RA4; if it is pulled low, that indicates that the switch is closed. No crystal required Most PIC circuits use a crystal for May 2002  27 Parts List – KnightRider 1 PC board coded 08105021, 210 x 72mm 1 heatsink, 19 x 19 x 10mm 1 2-way PC-mount screw terminal 1 snap-action PC pushbutton switch (S1) 1 M3 x 6mm screw and nut 4 adhesive rubber feet 1 350mm length of 0.8mm tinned copper wire Semiconductors 1 PIC16F84P (IC1) programmed with Knight.hex 1 LM358 dual op amp (IC2) 1 7805 regulator (REG1) 5 BC328 PNP transistors (Q1-Q4, Q6) 1 BC338 NPN transistor (Q5) 1 16V 1W zener diode (ZD1) 1 1N4002 diode (D1) 33 5mm red high-brightness LEDs (LED1-LED33) Capacitors 1 100µF 16VW PC electrolytic 5 10µF 16VW PC electrolytic 1 0.1µF MKT polyester (code 100n or 104) 1 15pF NP0 ceramic (code 15p or 15) Resistors (0.25W, 1%) 1 68kΩ 1 47kΩ 1 22kΩ 2 10kΩ 1 4.7kΩ 2 1kΩ 4 680Ω 8 150Ω 1 10Ω 2 50kΩ horizontal trimpots (code 503) (VR1,VR2) the internal oscillator but this circuit does not require precision timing. For these situations, the PIC can be set up as a relaxation oscillator (similar to the 555) whereby a capacitor connected to pin 16 is charged from the positive supply (+5V) via a resistance and then discharged via an internal transistor. In this case we connected a 15pF capacitor to pin 16, charged from +5V via trimpot VR1 and a 4.7kΩ resistor. The classic sawtooth waveform of the oscillator can be seen in the top trace of Scope 1. 28  Silicon Chip Interestingly, the waveform at pin 15, OSC OUT, is not the same as at pin 16. Instead it is a square wave at one quarter the frequency. Frequency of operation can be varied from about 4MHz when VR1 is set to minimum resistance, down to about 500kHz when VR1 is at maximum resistance. Transistor Q6 and its associated resistors provide a reset for IC1 when the supply is below a certain voltage. This ensures correct start up for IC1 when power is applied. The circuit can be powered from a 12V battery, DC power supply or DC plugpack. Diode D1 gives reverse polarity protection while the 10Ω resistor and zener diode ZD1 provide transient protection. The 12V supply is filtered with a 100µF capacitor before being applied to REG1, a 5V regulator. Its output is decoupled with a 10µF capacitor to ensure stability. Software The software required to provide the various LED display patterns was written to minimise the number of instruction codes. This is because there are only 1024 bytes of memory and we would quickly run out of space if we were to list each individual LED and its state during a pattern sequence. This normal approach involves using a lookup table. Instead of using a lookup table, the software makes note of the fact that much of the sequence is repetitive and only a short list of LED switching operations is required. This list is used in various ways to generate the required pattern. The efficiency of this approach is evident by the fact that we managed to include some 12 distinct patterns into the software with some space left over. In contrast, if we had used a lookup table it would have only allowed one or maybe two patterns at the most. The full software listing for the KnightRider is called knight.asm; it (and the .hex file) is available from our website – www.siliconchip.com.au Construction The KnightRider is constructed on a PC board coded 08105021 and measuring 210 x 72mm. Begin construction by checking the PC board for shorted tracks or any breaks in the copper pattern. Check the pattern against the published artwork to verify that it is correct. Repair any defects on the PC board before starting assembly. Fig.2 shows the component overlay for the PC board. First, install all the links on the PC board. Then install the resistors, using the colour codes shown in the parts list as a guide to selecting the values. You can also check each value with a digital multimeter to be sure that you have the correct resistor for each position. The diodes can be installed next, taking care not to confuse zener diode ZD1 with standard diode D1. IC1 is mounted using a socket while IC2 can be soldered directly into the PC board. The 3-terminal regulator is mounted horizontally, so carefully bend the regulator leads before inserting them into the relevant holes on the PC board. It is mounted onto a small heatsink and secured with an M3 screw and nut. When installing the five transistors, make sure that the BC338 is placed in the Q5 position. Next, install the capacitors. The codes of low value types are listed in the parts list. The electrolytic capacitors will have their values marked in µF; be sure to orient them correctly. Switch S1 should be installed with the ‘flat’ side oriented as shown Fig.2. Insert LED 33 with the anode (longer lead) placed toward the VR1 side of the PC board. Trimpots VR1 and VR2 and the PC-mount terminal block can then be soldered into place. Finally, the 32 LEDs can be installed along the edge of the board. They are placed with the anode leads (longer lead) to the left. You can preform all the LED leads by cutting a length of cardboard 10mm wide. Place the LED across this with the anode to the left and bend the leads downward. This will allow the LEDs to be inserted into the PC board with sufficient clearance for the LED body to just protrude over the front edge of the PC board. Check your work carefully for correct orientation of the capacitors, for the correct transistors in each place and the correct orientation of IC2 and the socket for IC1. Do not install IC1 yet. Testing Now apply power to the +12V and www.siliconchip.com.au TABLE 1: PATTERNS AVAILABLE K Type 1 Scan LEDs move from left to right and then right to left yes 2 Scan LEDs move symmetrically from centre to outside and from outside to centre yes 3 Scan LEDs move symetrically from centre to outside yes 4 Scan LEDs move symetrically from outside to centre yes Patterns 1, 2, 3 & 4 selected in sequence with change every power up yes# 1 6 Medley 8 cycles of pattern 1 16 cycles of pattern 2 16 cycles of pattern 3 16 cycles of pattern 4 7 Chaser LEDs chase from right to left yes ## 8 LEDs chase from left to right yes 9 Strobe All LEDs on then off at regular rate 10 Strobe All LEDs on then off at random rate yes 11 Random LEDs lit at random until all on, then off at random until all off yes 12 Medley 100 cycles of pattern 7 100 cycles of pattern 8 20 cycles of pattern 9 20 cycles of pattern 10 2 cycles of pattern 11 yes+ 13 Brake All LEDs on at power-up for 18s minimum then off at random until all off no 14 Brake All LEDs on at power up and remain on until power off no++ yes 1 BRIGHT 08105021 C 2002 # ## + ++ Chaser PATTERN 5 Scan Pattern Description     Repeat SPEED No. (of selected pattern) (Medley repeats of patterns 1, 2, 3 & 4) (Medley repeats of patterns 7, 8, 9 & 10) (only lights again after power off and on again) GND +12V 0V supply terminals and measure the voltage between the metal tab of REG1 and pin 14 of the IC1 socket. This should be +5V. If this is correct, disconnect power and insert IC1, making sure it is oriented correctly. Apply power again and check that the LEDs start to light up and produce a chasing pattern. The initial pattern is the KnightRider chaser (Pattern 1) with the LEDs moving from left to right and from right to left. www.siliconchip.com.au Check that you can adjust the speed with trimpot VR1 A KNIGHT RIDER and vary brightness with VR2. You can test for the other Full-size PC board artwork. Use this to check patterns by pressing the commercial boards or to make your own board. pattern switch. Each time you press the pattern switch, LED33 trimpot (VR1) so that you can easily count the number of flashes from will flash the required number of times and then the selected pattern sequence LED33. will start to run. Table 1 shows the 14 patterns You may need to adjust the speed available. SC May 2002  29