Function Generator

The FunGen Function Generator design utilises the Exar 2206 IC to produce Sine, Triangle and Square waves with adjustable frequency. Its features include:

Output Waveforms: TTL Square Wave and selectable Sine or Triangle Wave

Output Amplitude: Square Wave: TTL Output, Sine/Triangle: 0Vp-p to approximately 6Vp-p.

Output Frequency: 25Hz to over 250kHz 

The design includes a buffered virtual ground circuit provided by an LM741, LM318 or similar Op Amp, which sets a fixed voltage half way between the input voltage and ground. This is then used as the virtual ground for the sine and triangle wave outputs from the "WAVE_OUT" connector, providing an output centred around 0V.

A 74HC04 or 74LS04 Hex Inverter is used to buffer the Square Wave output, decreasing the rise and fall time of the square wave output.

The amplitude and frequency adjustment pots are mounted on the board for easy adjustment. An ON/OFF switch, Waveform selector switch and Frequency range switch are also mounted on the board.

Schematic:

Components Required:

IC1,   XR2206 

IC3,   LM741 or LM318 Op Amp

IC2,   74xx04 Hex Inverter

IC4,   LM7812

IC5,   LM78L05

C1,   100uF (or 10uF) Capacitor

C2,C5,C6,C7,C10,  1uF Capacitor

C3,C4,   0.1uF Capacitor

C8,   0.22uF Capacitor

C9,   2.2nF Capacitor

D1,   1N4001 Diode

R4,   200Ω 1% Resistor

R1,R5,R7,   1kΩ Resistor

R2,R3,R6,   10kΩ Resistor

R8,R9,   100 Ω Resistor (optional)

pot1, pot3,   50kΩ Pot

pot2,   250kΩ Pot

two Sliding Switches

3mm or 5mm LED

two,   Dual Screw Terminal

Multi PIC Programmer

This Multi PIC Programmer works as a usual JDM Programmer,  This Multi PIC Programmer works as a usual JDM Programmer. When the switch-2 is on, this Multi PIC Programmer changes into VPP-FIRST mode.

The switch-2 will be used only when both INTOSC and internal MCLR options are selected (PIC12Cxxx,PIC12CExxx,PIC12F629, and PIC12F675,etc. Please refer to the data sheet of each PICs for more details).                                                                                                                                                                       Read more

Schematic:

Components Required: 
R1,  1.5k ohm 
R2,  10k ohm 
R3,  1k ohm 
R4,  100 ohm
R5,  10k ohm
D1-D4,  1N4148 
D5,   5.1v Zener
D6,  6.2v Zener 
D7,  Red LED 
C1-C2,   100uF, 16v Electrolyte
C3,   100nF Ceramic
Q1-Q2,  BC54
Q3,   BC557 
40 Pin ZIF Socket
 SW1, sliding switch
 SW2, on/off switch
 BD-9 Female

The Circuits and PCB layouts can be downloaded from here

Automatic emergency light

Features:

• It is highly bright due to the use of white LEDs.

• The light turns on automatically when mains supply fails, and turns off when mains power resumes.

• It has its own battery charger. When the battery is fully charged, charging stops automatically.

Description:

The circuit comprises two sections: charger power supply and LED driver.The charger power supply section is built around 3-terminal adjustable regulator (IC1) LM317, while the LED driver section is built around transistor BD140(T2).

In the charger power supply section, input AC mains is stepped down by transformer to deliver 9V, 500mA to the bridge rectifier, which comprises diodes (IN4007x4). Filter capacitor (25v/1000uf) eliminates ripples. Unregulated DC voltage is fed to input pin 3 of IC1 and provides charging current through diode IN4007(D5) and limiting resistor (16ohm) R3. By adjusting preset 2.2K(R16), the output voltage can be adjusted to deliver the required charging current.

When the battery gets charged to 6.8V, zener diode conducts and charging current from regulator (IC1) finds a path through transistor BC547(T1) to ground and it stops charging of the battery. 

The LED driver section uses a total of twelve 10mm white LEDs. All the LEDs are connected in parallel with a 100-ohm resistor in series with each. The common-anode junction of all the twelve LEDs is connected to the collector of pnp transistor T2 and the emitter of transistor T2 is directly connected to the positive terminal of 6V battery. 

The unregulated DC voltage, produced at the cathode junction of Bridge(Diodes), is fed to the base of transistor T2 through a 1k resistor. When mains power is available, the base of transistor T2 remains high and T2 does not conduct. Thus LEDs are off. On the other hand, when mains fails, the base of transistor T2 becomes low and it conducts. This makes all the LEDs (LED1 through LED12) glow. The mains power supply, when available, charges the battery and keeps the LEDs off as transistor T2 remains cut-off. During mains failure, the charging section stops working and the battery supply makes the LEDs glow. 

Schematic:

Components:

 D1-D5,   1N4007

 D6,  6.8v Zener

 TR1,   9v 500mA transformer

 IC1,   LM317

 C1,  1000uF/25v electrolyte capacitor

 T1,   BC547

 T2,   BD140

 G1,   6v 4.5ah battery

 R1,   180 ohm

 R2,   1.2K ohm

 R3,   16 ohm  5watt

 R4,   1K ohm

 R5-R15,R17,  100 ohm  0.5 watt

 R16,  2.2K trimpot

 LED1-12,   10MM white

 

      

RS-232 level converter

This is a basic RS-232 transmit/receive circuit that is necessary for PIC microcontrollers to communicate with a PC serial port. The PIC microcontroller operates at TTL levels (0-5 Volts). The MAX233 IC allows you to convert microcontroller voltages to RS-232 compatible levels with no required external components.

Schematic:

 

Components Required:

Max233 IC

DB-6 Female

1uF/25v Electrolyte Capacitor

20 pin IC Socket

JP1, 2 pin connector/jumper

How to make PCBs using toner transfer method

First design the schematic and convert it into board layout, in Eagle layout. Making schematic first helps because Eagle will show you clearly if you make any mistakes with the PCB.

Print the pcb traces out onto semi glossy photo paper. 

Then quickly take this paper, cut out your design and place it face down onto some blank PCB board. Then use an iron and press the design on to the board. Use a lot of pressure and ensure all traces of the design make good contact with the blank PCB. Keep it pressed for at least three minutes. After removing the paper you get something like this:

 

sorry about the flash on image 

There are many alternatives for etching liquids, and you can use the one that suits your taste. I use ferric chloride: it’s cheap, can be reused many times, and doesn’t require heating. Actually, moderate heating can speed up etching.

 

Do not directly heat it, use hot water and put the ferric chloride container in it to speed up the process.

After etching the pcb looks like:

A few drops of thinner (nail polish remover works well) on a pinch of cotton wool will remove completely the toner, bringing back the copper surface. Rinse carefully and dry with a clean cloth or kitchen paper. After drilling your home made pcb is ready to use.