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:
'POWER' LED.
'HIGH' LED - reporting Logic State +Vcc (TTL 5V, CMOS 3-15V, Logic 1, True).
'PULSE' LED - reporting an Oscillating State e.g. Clock or Step Change (Up or Down).
'LOW' LED - reporting Logic State Gnd (TTL 0V, CMOS 0V, Logic 0, False).
2-way Toggle Switch. Positions: 'CMOS' 40'xx Series and 'TTL' 74'xx Series, for selecting between the two chip sets.
A 2-way insulated power cable terminating in one Red and one Black crocodile clip for linking to the circuit under test's power supply to ensure a common ground. No battery required.
Logic Probe Case with Red / Black Croc. Clips Power Cable.
Logic Probe Case (open) with 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.
PARTS LIST FOR CMOS LOGIC PROBE
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!
Capacitors
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 µF 16V Tantalum Bead (WW35) - 45p
C4 10 µF 10V Electrolytic (JA75S) - 8p
To smooth spikes from the circuit power supply.
Semiconductors
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
Miscellaneous
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 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:
x4 LED Holes for the four RED 5mm LED's. With 5mm LED Clips to hold them in place (cheap chrome bezzels are now available which would look more professional). RED LED's (12p) are generally a few pence cheaper than Green, Orange, or Yellow because of the relative complexities of the manufacturing process. Blue LED's are phenomenally expensive to produce (91p!).
x1 Hole for the toggle switch. Which should be attached using the Hex. Nut and crinkly Shake (to stop the switch loosening after constant use).
x1 Hole for the Probe Case. Hacksawed to length and glued in place.
Maplin Electronics