Sagar 001
In the past, I have uploaded many tutorials on how to design a perfect preamplifier. And in the race for the best one, I am developing some new preamps this time, all of which are based on a single IC. The interesting thing is that we can control these preamps through a web server through WIFI. Today, we have here, PT2258, a 6-channel electronic volume controller IC, designed for the new generation of AV Multi-Channel Audio Systems.
So this is an all-digital system in which we got an I2C Control Interface, an attenuation range of 0 to -79dB at 1dB/step, low noise, and high channel separation. This is very interesting because now we do not need those big circuits and potentiometers to adjust volume through any microcontroller.
Housed in 20 pins, DIP or SOP, PT2258’s pin assignments and application circuit are optimised for easy PCB Layout and cost-saving advantages. Although the system may have some disadvantages because everything is based on an IC and some external components, the flexibility to work with this system decreases on the hobbyist end. The PCBs are fabricated from NEXTPCB, they have done the perfect job.
This type of IC is used in surround sound-type things, where we need to adjust the volume of more than two channels. Some of the listed features of PT2258 are:
- Least External Components
- Attenuation Range: 0 to -79dB at 1dB/step
- Operating Voltage: 5 to 9 V
- Low Noise, S/N Ratio>100dB (A-weighting)
- High Channel Separation
- I2C Bus Control Interface
- Selectable Address
- 6-Channel Outputs
Components Required:
- PT2258
- ESP12E/ESP8266
- 47uf/10uf electrolytic capacitors
- 10K/100K resistors
- 3.3V AMS1117 regulator
- Some pin headers
- 5V power source
Circuit diagram:
I have taken the reference from the circuit given in the datasheet. Here, you can see that the IC has 6 channels. We need 6 inputs and 6 outputs. If there is no signal, the input is referenced to ground by a 100K resistor, and a 10 μF coupling capacitor is also present, which behaves like a filter with the resistor arrangements. Because the circuit is fixed, the only controlling input to the IC is the I2C bus, allowing us to connect any microcontroller.
Now, here is the circuit diagram I used for the IC. Since we have only one I2C bus, the ESP8266 supports this protocol, and it has Wi-Fi, so we can utilise these features. There are a lot of revisions you will find on the internet using the same code and libraries for this DSP. But now with this microcontroller and web server, we have eliminated a lot of components. No need to print the data on screen, and no need for external push buttons. However, there is always an option to do this because most of the microcontroller's GPIOs are available.
PCB Design:
I want to keep the system minimal, the reason is that there are analogue and digital parts that are on the same circuit board, and the data is travelling through SCL and SDA lines. The audio is not such a high frequency, but we should follow proper guidelines. The best thing is to route these digital signals away from any analogue signal and surround them with ground planes.
For the assembly, because I have used mainly the THT components, which can be soldered by hand, moreover, only the ESP8266 is the one using SMD pads, where you may get some issues. Still, I always recommend soldering the SMD first, then moving to the THTs, and finally to the header part. In this way, with minimum time and effort, you can solder this board. All the links to FILES: GERBER/BOM/CPL are here.
The same is implemented here in the design; I use ground fills on both layers, which can be connected with vias and ground stitches. Moreover, the LDO is in the middle, powering the ESP8266, and all other systems run at 5V. The signal may get interference if the supply used is SMPS, so try to go with batteries or a good power adapter with EMI shielding to reduce the overall noise. The PCB features programming headers on the bottom layer, where all...
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