The MY-68 digital multimeter
The MY-68 is a cheap, quality auto-ranging digital multimeter with high resolution, good accuracy and many useful features such as data hold, auto power off, tilt back stand, test leads holder and so on.
The instrument performs AC/DC voltage, AC/DC current, resistance, audible continuity, diode, transistor, frequency and capacitance measurements, employing a 3 3/4 digit, 3260 count IC (KAD7001). The MY68 has a large LCD display and an analog bargraph. With a price of under 50$ it is really a bargain - a good, precision instrument for both the amateur and professional.
MY-68 schematic diagram (GIF)
Operating instructions
The meter has four input jacks. Connect the black test lead to the COM (black) input and the red lead to one of the (red) input jacks corresponding to the function you want to use. To avoid damage to the multimeter, don't apply input voltages and currents which exceed the following limits:
| Function | Red lead connection | Input limits |
|---|---|---|
| DCV/ACV | VΩF | 1000V DC, 750V rms AC |
| kHz | VΩF | 250V DC or rms AC |
| Ω/Buzzer/Diode | VΩF | 250V DC or rms AC |
| µA/mA | mA/Cx | 300mA DC or rms AC |
| nF/µF | mA/Cx | 300mA fuse protected |
| A | A | 10V DC or rms AC |
The range control button
The ranges for AC/DC voltage, AC/DC current (µA and mA only), resistance and frequency can be selected manually or handled by autoranging. Push this button to choose the range control mode and the desired ranges.
The DATA-HOLD button
When this button is pushed, the display will show the last reading and the "D-H" symbol will appear until pushing it again. Data holding will be canceled automatically when the function switch is rotated.
AC/DC current or Buzzer/Diode selecting button
Push this button to select AC or DC current measuring mode when the function switch is set at the µA, mA or A positions, or to select Buzzer/Diode mode when the function switch is set at Buzzer/Diode position.
Measuring voltage
1. Connect the black test lead to the COM jack and the red test lead to the V/Ω/F jack.
2. Set the function switch at V- or V~ range and connect the test leads across the voltage source or load under measurement.
3. Read the LCD display. The polarity of the red connection will be indicated when making a DC measurement.
Measuring current
1. Connect the black lead to the COM jack and the test lead to the mA/Cx jack when measuring currents of max. 300mA. For the 10A range, move the red lead to the A jack.
2. Set the function switch at µA, mA or A range depending on your task, and push the ~/- button to select DC A or AC A measuring mode.
3. Connect the test lest leads in series with the circuit.
4. Read the LCD display. The polarity of red lead connection will be indicated when making a DC measurement.
Measuring resistance
1. Connect the black test lead to the COM jack and the red test lead to the V/Ω/F jack. The polarity of the red lead connection is positive.
2. Set the function switch at the Ω range and connect the test leads across the resistance under measurement. For resistances above 3.2MΩ, the meter may take a few seconds to stabilize the reading. This is normal for high resistance measuring. When the input is not connected, i.e. at open circuit, the figure “OL” will be displayed for the overrange condition.
3. When checking in-circuit resistors, make sure the circuit under test has all power removed and all capacitors are fully discharged.
Measuring capacitance
1. Connect the black test lead to the COM jack and the red test lead to the mA/Cx jack. The polarity of the red lead connection is positive.
2. Set the function switch at the nF or µF position.
3. Connect the test leads across the capacitor under measurement, keeping in mind the polarity of the capacitors. When checking in–circuit capacitors, be sure that the circuit has all power removed and all capacitors are fully discharged. The range control mode in capacitance measurement is manual ranging and only two ranges (326nF and 32.6µF) are provided. If the Range Control Button is used in this mode, the decimal points may be at incorrect positions.
Note: at the nF range, if the capacitor to be measured is not connected to test lest leads, the LCD may not read zero, but a few counts - these counts have to be subtracted from the results.
Measuring frequency
1. Connect the black test lead to the COM jack and the red test lead to the V/Ω/F jack.
2. Set the function switch at the kHz position and place the test leads to the measuring point. The input voltage should be between 200mV and 10V rms AC. If the voltage is more than 10V rms, the reading will not be accurate.
Continuity and Diode test
1. Connect the black test lead to the COM jack and the red test lead to the V/Ω/F jack. The polarity of red lead connection is positive.
2. Set the function switch at the Buzzer/Diode position and push the Buzzer/Diode button to select continuity or diode test mode.
3. In continuity testing, if continuity exists (i.e., the resistance is less than about 50Ω), the built-in buzzer will sound. If the diode test mode is selected, connect the red and black leads to the anode and cathode of the diode under test. The forward voltage drop of this diode in Volts will be displayed.
Transistor test (hFE)
1. Set the function switch at the hFE position.
2. Identify whether the transistor is NPN or PNP type and locate the emitter, base and collector leads. Insert the transistor's leads to be tested into the proper holes of the socket on the front panel.
3.The LCD display will show the approximate hFE value at the test condition: base current of 10µA and Vce of 3.2V.
Technical specifications
Note: The MY-68 digital multimeter is made by a dozen of manufacturers, and the user manuals for different versions present different accuracy ranges for their products. For ex. some manuals describe the maximum frequency range of the MY-68 as 150KHz with ±(1.0% of rdg + 2digits) accuracy - others as 200KHz with ±(2.5% of rdg + 3 digits) accuracy. So make sure you consult your meter's user manual for your instrument's exact specifications. The following specs are taken from a variant sold on the US market.
DC Voltage (Auto ranging)
Input impedance:
- 326mV range: more than 100MΩ
- all other ranges: 10MΩ
| Range | Resolution | Accuracy |
|---|---|---|
| 326mV | 0.1mV | ± (0.5% of rdg + 2 digits) |
| 3.26V | 1mV | ± (0.3% of rdg + 2 digits) |
| 32.6V | 10mV | ± (0.3% of rdg + 2 digits) |
| 326V | 0.1V | ± (0.3% of rdg + 2 digits) |
| 1000V | 1V | ± (0.5% of rdg + 2 digits) |
AC Voltage (Auto ranging)
Input impedance: 10MΩ
Frequency range:
- 40Hz to 200Hz for the 3.26v range
- 40Hz to 1000Hz for all other ranges.
| Range | Resolution | Accuracy |
|---|---|---|
| 3.26V | 1mV | ± (0.8% of rdg + 3 digits) |
| 32.6V | 10mV | ± (0.8% of rdg + 3 digits) |
| 326V | 0.1V | ± (0.8% of rdg + 3 digits) |
| 750V | 1V | ± (0.8% of rdg + 3 digits) |
DC Current (Auto ranging for uA and mA)
| Range | Resolution | Accuracy |
|---|---|---|
| 326µA | 0.1µA | ± (1.2% of rdg + 3 digits) |
| 3260µA | 1µA | ± (1.2% of rdg + 3 digits) |
| 32.6mA | 10µA | ± (1.2% of rdg + 3 digits) |
| 326mA | 0.1mA | ± (1.2% of rdg + 3 digits) |
| 10A | 10mA | ± (2.0% of rdg + 5 digits) |
Overload Protection: 300mA fuse for mA ranges and a 10A fuse for the 10A range.
AC Current
Frequency Range: 40Hz to 1000Hz
Response: Average in rms of sine wave
| Range | Resolution | Accuracy |
|---|---|---|
| 326µA | 0.1µA | ± (1.5% of rdg + 5 digits) |
| 3260µA | 1µA | ± (1.5% of rdg + 5 digits) |
| 32.6mA | 10µA | ± (1.5% of rdg + 5 digits) |
| 326mA | 0.1mA | ± (1.5% of rdg + 5 digits) |
| 10A | 10mA | ± (3.0% of rdg + 7 digits) |
Resistance
Open circuit voltage:
- 400 ohm range: 2.6V
- all other ranges: 1.3V.
Note: On the 200MΩ range, if test leads are shorted, the display will show 10MΩ - this value should be subtracted from the reading.
| Range | Resolution | Accuracy |
|---|---|---|
| 326Ω | 0.1Ω | ± (0.8% of rdg + 3 digits) |
| 3.26KΩ | 1Ω | ± (0.8% of rdg + 1 digits) |
| 32.6KΩ | 10Ω | ± (0.8% of rdg + 1 digits) |
| 326KΩ | 100Ω | ± (0.8% of rdg + 1 digits) |
| 3.26MΩ | 1KΩ | ± (0.8% of rdg + 1 digits) |
| 32.6MΩ | 10KΩ | ± (1.2% of rdg + 2 digits) |
Frequency
Sensitivity: 200mV rms up to 50 KHz, 1V rms for 50KHz to 200KHz
| Range | Resolution | Accuracy |
|---|---|---|
| 32.6KHz | 10 Hz | ± (1.2% of rdg + 3digits) |
| 200KHz | 100 Hz | ± (2.5% of rdg + 3digits) |
Capacitance
| Range | Resolution | Accuracy |
|---|---|---|
| 326nF | 0.1nF | ± (3.0 % of rdg + 5 digits) |
| 32.6µF | 10nF | ± (3.0 % of rdg + 5 digits) |