The system is based on the ATtiny26 microcontroller. The current measurement is performed indirectly across 1R resistors connected to the cathode circuit of the radio tube, as shown in Figure 2. In order not to significantly affect the operating point of the tube, the resistor should have a low resistance. The voltage corresponding to the current is amplified 10 times by the amplifiers U1 and fed to the analog-to-digital converter built into the microcontroller U2. The measurement result is displayed on the LCD screen with a resolution of 2 lines x 8 characters. Depending on the setting of jumper X3, measurements can be made in one channel (monoblock) or two channels (stereo amplifier).

Transistor Q1 with associated components controls the voltage relay with an anode delay time set to 60 seconds. The countdown is displayed on the LCD.

The power supply system is typical and does not require a detailed description. A small 2VA transformer, galvanically isolated from the amplifier circuit, was used as a power source. This increases the flexibility of applications, but each time with a stereo amplifier, check to see if the connection will cause the amplifier to malfunction.

Potentiometer RV1 allows you to set the contrast, resistors R7 and R8 are responsible for the intensity of the backlight. The model uses a backlit display.

The system is assembled on a double-sided printed circuit board, the assembly diagram of which is shown in Figure 3. Typical assembly method: first we mount the SMD elements, then the through-hole elements, then the LCD, which is the mechanical base of the system and is connected to the plate using a 2-way socket. x 2.54 mm. Display mounting holes are used to assemble everything in the amplifier. Make sure they are not connected to system ground. In this case, it must be installed with insulated couplings to avoid ground loops in the system.

The system does not require starting, you only need to set the display contrast and select the number of measuring channels.

The display mounting holes are used to mount the whole thing in the amplifier. Make sure that they are not connected to the ground of the system. If so, installation with insulated sleeves is required to avoid ground loops in the system. It is also necessary to program the processor with the file: IA_Minimeter.hex and set the fusebits: RCInt = 1MHz, CKSEL3, 2, 1 = 0001; CKSELO = 1; SUTO, 1 = 0; BODEN, BODLEVEL = 0; others = 1.