Beep - a sounding logic probe/tester [140410]

I find it pretty annoying when I use a multimeter and look at the display only to find out that I accidently disconnected the probe from the pad.That's where the logic probe, we dubbed Beep, comes in. Instead of using a display, it uses a buzzer to represent the Signal Under Test (SUT) with sound.

I find it pretty annoying when I use a multimeter and look at the display only to find out that I accidently disconnected the probe from the pad.

That's where the logic probe, we dubbed Beep, comes in. Instead of using a display, it uses a buzzer to represent the Signal Under Test (SUT) with sound.

Beep has two connectors, one is used for its power supply taken from the circuit under test and the other connector is used for the SUT. When the second connector (for the SUT) isn't connected to anything or is connected to a circuit with too high impedance, the buzzer remains silent. If the connector is connected to something, the buzzer will begin to buzz.

When the SUT is logic 0, the buzzer will buzz with a low tone. If the SUT is logic 1, the buzzer will buzz at a high tone. If the SUT has a frequency, a frequency divider with a division factor of 256, 1024 or 2048 (actually a 12-stage binary ripple counter) will kick in in order to lower the frequency to a audible frequency. The division factor can be changed by use of the switch.

Beep’s components are mostly taken from the Elektor.Labs Preferred Parts (ELPP) library. Farnell and RS order codes can be found there.

Project Elements

140410-52a.jpg (JPG, 143.95 KB)

140410-1-v1.2-multitester-circuit-diagram.pdf (PDF)

140410-1-v1.2-multitester-pcb.pdf (PDF)

Discussion (2 comments)

Ahad Iran 5 years ago

Hi, I'm a great project for me, but I'm residing in Iran and I can not buy it. I'm sad for this project.

0 Comment(s)

NECV20 10 years ago

When I test this circuit, I get a shortcut when I test a frequency of 100 kHz.

If I take the SOT-probe off the circuit after the shortcut occurs, pin 13, 14, 15 of IC1 stays high and the shortcut persists. The only way to resolve this, is to cut the powersupply from the circuit.

Even if I take IC1 off the PCB, and power it with 3.3V, testing on high or low level sometimes (about 1 in 10 times) results in a shortcut.

Is R7 not a 0 Ohm resistor?

NECV20 10 years ago

I checked your idea about the diodes. Sorry, but that is not working either. After power up outputs 2-4 and 6-10 of the 4050N are high and outputs 12-15 are low. So there is always one pair high, disabling any sound beeing produced. The only way it might work is to throw the 4040N out of the design, disconnect 12-15 of the 4050N to the buzzer and turn the diodes around, so the anodes are connected to the buzzer. But I am not going to check it. This project ended up in my bin of electronic waste.

BAECK 10 years ago

The ELCO's are not 100% correct used. In some situations have the ELCO's an inverse polarity. This degrades the dielectric layer in the ELCO. In the assembly photo, I found 100V ELCO. 100V ELCO has a stronger dielectric layer then e.g. 16V ELCO On the other side, the switching times of the 4050 are very short for this 4.7 µF ELCO's. For 5V is the rise time typically 80 ns, the fall time 30 ns. Continuous switching of IC2 generates a lot of dissipation in this situation. The probability for overheating and damage of the IC is great. Changing the ELCO's with diodes (all cathodes connected to the buzzer) works better (this is not checked). The buzzer is also polarized, thus also better for the buzzer.

NECV20 10 years ago

Hello BBEC, Sorry, translation error on my side in my comment; where you read shortcut, I mean short-circuit! I did some further measurements on the circuit. All with no power applied and measuring with a multi-meter. If I remove IC2, the 4050, on pins of the IC-soscket 2, 4, 6, 10, 12 and 15 I measure a capacity of 4.7 uF. That is oké. But if I place IC2 in its socket, on all above mentioned pins I measure 15 uF. Does all the buffers in the 4050 have a common ground or power connection? If that is being the case, then current can rush from one buffer output (high) to other ones (low). Furthermore, the datasheet states that the outputs should not be made to deliver more than 12 mA for a "longer" period. Connecting them directly to a capacitor may seem to be asking for trouble. I look forward on your comments on the "strange connections". YS, NECV20