CMOS / TTL Logic Probe Project.

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The Magazine Project design I used was for a CMOS (Voltage: 3-15V) and TTL (Voltage: 5V) Logic Probe. Used for diagnosing faults in digital logic circuits such as gates. With:

Logic Probe Case with Red / Black Croc. Clips Power Cable.

Logic Probe

Logic Probe Case (open) with Circuit.

Logic Probe and Circuit

The circuit was soldered onto a 9 x 37 hole vero-board which was cut to size using a hacksaw then filed to smooth the edges. This gave 9 fully conducting rows of holed copper. A 'spot face cutter' tool was required to 'halve-drill' holes in the vero-board to stop the whole track row length conducting. For two sides of a IC for example.

Spare 2-way strips of ribbon cable was used to connect the circuit board to the 4 LED's, and 2-way switch. These were covered in insulating tape to stop short circuits between the board and components. The 2-way insulated power cable terminated in the circuit board. And one final wire went to the probe its self.


Resistors - Min Res - ALL 9p each
R1,8		10k (Brown Black Orange)			3 off		(M10K)
R2,4		2.2k (Red Red Red)				3 off		(M2K2)
R5,10,11	4.7k (Yellow Violet Red)			3 off		(M4K7)
R6,13		8.2k (Grey Red Red)				2 off		(M8K2)
R7		470k (Yellow Violet Yellow)				(M470K)
R9		270W (Red Violet Brown)					(M270R)
R12		16k (Brown Blue Orange)					(M16K)
Colour Code Convertor PC Windows Programme. Very good and easy to us. I recommend it!

C1,2		10 nF (104Z) Ceramic 10			2 off		(WX44X) - 7p
All ceramics are measured in pico farads. So 104 = 10,000 pico farads = 10 nano farads. 
See Engineering Notations for description of measurements.
C3		4.7 F 16V Tantalum Bead					(WW35) - 45p
C4		10 F 10V Electrolytic					(JA75S) - 8p 
To smooth spikes from the circuit power supply.

IC1		LM393N Voltage Comparator					(UH30H) - 54p 
IC2		555 Timer - NE555N						(GH66W) - 37p
D1		Diode (to protect circuit in case power leads are connected back to front).
D2,5		5mm RED LED's						(WL29E) - 12p 
		With 5mm LED Clips				4 off		(YY40T) - 8p 
	 [OR]	5mm LED Cliplite Covers			4 off		(YH54J) - 21p	
	 [OR]	5mm LED Chrome Bezzels, top quality	4 off		(N89AX) - 87p

LK1-11		Wire links between circuit tracks.
SW1		SPDT Ultra Min Tggle - 5.2mm Mounting Hole		(FH98G) - 1.49
CN1		Gold Croc Clip Red						(FS53J) - 52p
CN2		Gold Croc Clip Black					(FS55K) - 52p
		One Meter of 2-way Cable for power lead.
		Small moulded black plastic case			(FT31) - 99p
			124mm long by 33mm wide by 30mm deep
		Logic Probe Tip - Long M3 bolt
		Legends (white transfer writing for case).
		Vero-board, 81 x 14 holes - Stripboard			(FL17T) - 4.99

All components available from Maplin Electronics on-line (through the Post or from there 40 UK Shops). The Logic Probe project was published in the Maplin Magazine.

Maplin Logo Maplin Electronics - postal retailer with shops of 12,000 quality Electronic Components and Items, large stock, own catalogue. P&P 2.50, free over 35 incl. VAT.

Preparing the Case

All components were bought from Maplin Electronics including the Case [ Maplin Code FT31 - 99p ]. The legends next to the LEDs, Switch, and Logic Probe Name were applied using white transfers. Then set by painting a little varnish over each word using a paint brush. The following holes had to be drilled in the case: