Hi Friend
OK, Here are some of the projects which I built and now up & running.
Multitester- This ckt can be used to (a) test & diagnose fault in an audio equipment or in the audio portion of any electronic appliance (b) check electrical continuity with resistivity upto say 15K (c) test any general purpose transistor,indicating either 'Go' or 'NoGo' state (d) test any diode or LED, indicating whether the device is OK or fault and (e) check the condition of any electrolitic cap. It has 3 transistors (one PNP - 2N481/BC158B, which function as a switch and 2 NPN medium power audio transistors - BC148Bs. Unit is powered by two 'AA' type dry cells.
Blown fuse indicator (for home AC line)- I put a neon in series with a current limiting resistor across my home supply line. So the neon is 'on' in the normal way.Home distribution box fuse is in between the neon and few other discrete components connected to 'live' line.(We have 230V/50Hz house supply here). When the fuse blows, neon acts as a oscillator & will flash on & off indicating the fuse has blown.
'Fast Fuse' - I used a SCR to blow a fuse in my 5V PSU. It may look a bit daft, but it has two important advantages. The most obvious one is fuses don't blow just because the voltage rises. So that a fuse doesen't protect the ckt against excessive voltage,it only protects the PS against excesive current. The other point is that a fuse takes some time to blow, several milliseconds. That may not sounds like a long time but several hundred dollars worth IC's can be destroyed in only a 1/1000th of that time. The SCR operates faster getting the voltage down as soon as it reaches danger level (controlled by a Zener) & blowing the fuse.
Musical car reverse horn - Using UM and LM386.
Battery level indicators - with zeners, with LM3914 and with 741 op-amp
12V car battery charger - I used the ckt given in National Semiconductor data sheet for LM350).
Various LED displays - With LM339, CD4017, LM3914.
Auto heat limiter for my slodering Iron.
Logic Probe using 3 TTLs (7402,7473,7474) and LM339 quad op-amp.
Transistor lead identifier cum tester- Using 4 TTls,74193,7400,7420,7408 & NE555 timer IC
I'm planing for :
:idea:
Electronic Capacitence Meter - Main IC is NE556 with some close tolarance resistors & caps.
Analogue Frequency meter - (Using high gain op-amp CA3140 & a NE556 dual timer)
Solid-State Oscilloscope - ( The heart of this system is 10 X 20 LED matrix display. I'm little bit nervous to try this !. I need some confidence from guys like you) .
Thanks
Have a nice day!