Maximite Stepper Motor Interface

This simple circuit and program listing allows the Maximite microcomputer (SILICON CHIP, March-May 2011) to control a stepper motor. It could be expanded to allow for the control of multiple motors, with four of the Maximite’s external I/O pins used to control each motor with identical driver circuits. A ULN2003 Darlington transistor array (IC1) switches current through the stepper motor’s two windings in either direction. When one of the four Maximite output pins (8, 12, 16 & 20, corresponding to I/Os 19, 17, 15 & 13) goes high, the corresponding output pin on IC1 goes low, sinking current through a motor winding. Conversely, when these pins are high, the corresponding Darlington transistor is off and so no current flows through that portion of the winding.

Maximite Stepper Motor Interface Circuit Diagram: 

Stepper Motor
The centre tap of each motor winding is connected to a current source comprising PNP Darlington transistor Q1 and some resistors. The maximum current is determined by the resistive divider driving its high-impedance base, setting the base voltage to around 9.1V when it is fully on. By adding Q1’s base-emitter voltage (1.4V at 0.5A, as per the data sheet) we can determine that there will be around 1.5V across the 3.3O resistor (12V - 10.5V), resulting in a current of 1.5V ÷ 3.3O = ~450mA. Transistor Q1 must be fitted with a medium-sized flag heatsink (Jaycar HH8504, Altronics H0637) or larger to handle its maximum dissipation of (10.5V - 4.9V) x 450mA = 2.5W.

When one of the Darlington transistors switches off and current flow through the corresponding motor winding ceases, the inductive winding generates a back-EMF current which causes the voltage across that winding to spike. IC1 has internal “free-wheeling” diodes from each output to the COM pin, which is connected to the +12V supply. The back-EMF current flows back into the power supply and the voltage spikes are clamped at about 12.7V, so that the Darlington transistors do not suffer collector reverse breakdown, which might damage them.

A 470µF capacitor provides supply bypassing for the motor while a 47kO pull-up resistor and toggle switch/pushbutton S1 drives input pin 9 of the Maximite, allowing manual control of the motor direction. Table 1 shows the sequence in which the output pins are driven to turn the motor forward; the steps are run backwards for reverse operation. The delay between the steps determines the speed at which the motor rotates. The source code of the sample program is available for download from the SILICON CHIP website (maximite_stepper_motor.bas).

Universal PIC Programmer

This simple programmer will accept any device that's supported by software (eg, IC-Prog 1.05 by Bonny Gijzen at The circuit is based in part on the ISP header described in the SILICON CHIP "PIC Testbed" project but also features an external programming voltage supply for laptops and for other situations where the voltage present on the RS232 port is insufficient.

Universal PIC Programmer Circuit Diagram:

Programmer Circuit Diagram
This is done using 3-terminal regulators REG1 & REG2. The PIC to be programmed can be mounted on a protoboard. This makes complex socket wiring to support multiple devices unnecessary. 16F84A, 12C509, 16C765 and other devices have all been used successfully with this device.

Intelligent Presence Simulator

Intelligent Presence Simulator Circuit diagram. However effective a domestic alarm system may be, it’s invariably better if it never goes off, and the best way to ensure this is to make potential burglars think the premises are occupied. Indeed, unless you own old masters or objects of great value likely to attract ‘professional’ burglars, it has to be acknowledged that the majority of burglaries are committed by ‘petty’ thieves who are going to be looking more than anything else for simplicity and will prefer to break into homes whose occupants are away.

Rather than simply not going on holiday – which is also one solution to the problem (!) – we’re going to suggest building this intelligent presence simulator which ought to put potential burglars off, even if your home is subjected to close scrutiny. Like all its counterparts, the proposed circuit turns one or more lights on and off when the ambient light falls, but while many devices are content to generate fixed timings, this one works using randomly variable durations.

Intelligent Presence Simulator Circuit diagram:


So while other devices are very soon caught out simply by daily observation (often from a car) because of their too-perfect regularity, this one is much more credible due to the fact that its operating times are irregular. The circuit is very simple, as we have employed a microcontroller – a ‘little’ 12C508 from Microchip, which is more than adequate for such an application. It is mains powered and uses rudimentary voltage regulation by a zener diode.

A relay is used to control the light(s); though this is less elegant than a triac solution, it does avoid any interference from the mains reaching the microcontroller, for example, during thunderstorms. We mustn’t forget this project needs to work very reliably during our absence, whatever happens. The ambient light level is measured by a conventional LDR (light dependent resistor), and the lighting switching threshold is adjustable via P1 to suit the characteristics and positioning of the LDR.

Note that input GP4 of the PIC12C508 is not analogue, but its logic switching threshold is very suitable for this kind of use. The LED connected to GP1 indicates the circuit’s operating mode, selected by grounding or not of GP2 or GP3 via override switch S1. So there are three possible states: permanently off, permanently on, and automatic mode, which is the one normally used. Given the software programmed into the 12C508 (‘firmware’) and the need to generate very long delays so as to arrive at lighting times or an hour or more, it has been necessary to make the MCU operate at a vastly reduced clock frequency.

In that case, a crystal-controlled clock is no longer suitable, so the R-C network R5/C3 is used instead. For sure, such a clock source is less stable than a crystal, but then in an application like this, that may well be what we’re after as a degree of randomness is a design target instead of a disadvantage. Our suggested PCB shown here takes all the components for this project except of course for S1, S2, and the LDR, which will need to be positioned on the front panel of the case in order to sense the ambient light intensity.

The PCB has been designed for a Finder relay capable of switching 10 A, which ought to prove adequate for lighting your home, unless you live in a replica of the Palace of Versailles. The program to be loaded into the 12C508 is available for free download from the Elektor website as file number or from the author’s own website: On completion of the solder work the circuit should work immediately and can be checked by switching to manual mode.

The relay should be released in the ‘off’ position and energized in the ‘on’ position. Then all that remains is to adjust the day/night threshold by adjusting potentiometer P1. To do this, you can either use a lot of patience, or else use a voltmeter – digital or analogue, but the latter will need to be electronic so as to be high impedance – connected between GP4 and ground. When the light level below which you want the lighting to be allowed to come on is reached, adjust P1 to read approximately 1.4 V on the voltmeter.

If this value cannot be achieved, owing to the characteristics of your LDR, reduce or increase R8 if necessary to achieve it (LDRs are known to have rather wide production tolerances). Equipped with this inexpensive accessory, your home of course hasn’t become an impregnable fortress, but at least it ought to appear less attractive to burglars than houses that are plunged into darkness for long periods of time, especially in the middle of summer. (

R1 = 1k 500mW
R2 = 4k7
R3 = 560R
R4,R6 = 10k
R5 = 7k5
R 7 = LDR
R8 = 470k to 1 M
P1 = 470k potentiometer
C1 = 470µF 25V
C2 = 10µF 25V
C3 = 1nF5
C4 = 10nF
D1,D2 = 1N4004
D3 = diode zener 4V7 400 mW
LED1 = LED, red
D4 = 1N4148
T1 = BC547
IC1 = PIC12C508, programmed, see Downloads
RE1 = relay, 10A contact
S1 = 1-pole 3-way rotary switch
F1 = fuse 100 mA
TR1 = Mains transformer 2x9 V, 1.2 -3 VA
4 PCB terminal blocks, 5 mm lead pitch
5 solder pins


Solar Garden Light

This is a Solar Garden Light Circuit Diagram that consists of a very simple system garden lighting that can be done by using some common electronic parts and a small solar panel. The electronic design is simple yet very efficient, has the advantage of being solar powered, it requires only one transistor, one 2.5 volt solar panel and some other common electronic components you can remove junk.

Solar Garden Light Circuit Diagram:

Solar Circuit Diagram
This solar lighting system automatically turns on the LEDs when the solar panel detects no light turns off when the solar panel produces more than 1v and charges the battery when the panel produces more than 2.1V

The coils in this circuit require a core material F29 and they must be made with wire of 0.095 mm in core 2.6x6mm. "This circuit uses the system joule thief (joule thief) to provide voltage necessary for the LED, so other coils can be tested.

VGA Monitor Splitter and Extender

The circuit was designed to provide distribution, extension and splitting of personal computer video output to two or more monitors.
  • Super Video Graphics Array (SVGA) – defined in 1989 as a set of graphic standards that supports 800 X 400 resolution or 480,000 pixels with support for 256 colors or a palette of 16 million colors.
  • Pixel – short for picture element, is the smallest point or single item of information in a graphic image and the basic unit of programmable color on a computer image or computer display.
  • 2N3906 – a common PNP BJT transistor intended for medium voltage, lower current and power, which can operate at moderately high speeds, used for general purpose switching and low-power amplifying applications.
The circuit may also be called as video port expander, multiple monitor, PC video splitter, LCD Y splitter, etc. It provides the same high resolution image to several monitors using a single PC. Each line of the SVGA card of the analog output stage of PC contains 75 ohm impedance being obtained from the signal sources.

The transistors will not contribute as additional loads as they are having very high input impedances. The parameters being shared are the primary colors which consist of Red, Green and Blue, the horizontal synchronization and the vertical synchronization. Since the three ID connections are supposed to be connected to less advance and cheaper monitors, they can be excluded in the circuit.

VGA Monitor Splitter and Extender Circuit Diagram:

VGA Circuit Diagram
The PNP switching transistor 2N3906 forms the emitter-follower mode of ten transistors. They are utilized due to their low current having a maximum of 200 mA, low voltage with a maximum of 40 Volts, low cost, versatile and efficient, although they are not the best possible choice. It is preferable to use faster transistors when dealing with higher pixel rates because high input resistances will be supplied by higher gain.

The resolution entirely dictates the quality of a display system as to how many bits are used to represent each pixel and how many pixels it can display. To prevent RF interference on the circuit, as the monitor operates in radio frequency, a metal casing should enclose the splitter circuit and eventually be connected to ground.

The circuit will require a power supply of 5 Volts and a current around 600 mA. The DC components in the output signals will not be considered as drawbacks since the splitter is working well with 1024×768 15” and 800×600 monitors. The 2N3906 transistor is intended for amplifier functions and high-speed switching in industrial applications. Since there are many standards that have followed, all are employing the standards of SVGA since 1990 which includes the eXtended Graphics Array (XGA) of IBM, Super XGA (SXGA), SXGA+, Ultra XGA (UXGA) and Quad XGA (QXGA).

This video splitter will be suitable for tradeshows, in-store displays or classrooms where high quality video on multiple monitors is need; for support with LCD flat panel monitors and DDC2B protocol; in digital signage applications with perfect resolution; for supporting 1900×1200 resolution without degradation; for burn-in of monitors after repair; and for support of stereo audio as well. 

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