Browse over 10,000 Electronics Projects

FISHINO becomes Mega

FISHINO becomes Mega

RESET Circuitry

Fishino MEGA’s reset section is the same of the one found in Fishino UNO, that you already know; as previously hinted, it turns out to be more complicated than the one in Arduino MEGA, for the following reasons:

  • it is needed to reset both the ATmega and the ESP, at the pressure of the reset button, at the start and at the programming request on the part of the IDE.
  • in order to execute ATmega’s programming via WiFi, the ESP module must be able to reset the same ATmega, without having in turn to self reset itself.

 

Let us start from the DTR signal, that comes out of the USB/Serial (U1/CH340G) interface; as anticipated, this is put at a low level when the serial port is opened. By means of a C5 capacitor (ceramic 1 µF, as opposed to the 100 nF of the original one, used so to extend the reset pulse) a short pulse is generated and, once it is passed through the SMD RESEN jumper (when cutting it, it is possible to deactivate the autoreset), it reaches the “external reset” line, to which the reset button and the pin 5 on the programming connector (ICSP) are connected.

Differently from the original circuit, in the Fishino boards a diode (D2) is inserted between the RESET line and the ATmega’s pin. The purpose of this diode (and of the D3 diode we will see later) is the one to reset the ATmega only, withouth having however to convey the signal to the ESP as well.

In brief:



Advertisement1


  • by pressing the RESET button, or by connecting the serial, the reset pulse reaches both the ATmega (via D2) and the ESP (directly), thus resetting them both;
  • a signal on the ATRES-ESP line, that is generated by the ESP (in the case the reprogramming via WiFi has been enabled), reaches the ATmega’s reset line through D3 but, because of D2, it cannot propagate itself in the same ESP.

 

By means of this system we therefore gave the possibility to the WiFi module to control the ATmega’s reset line that, along with the SPI interface, enables its reprogramming without even the need of a preloaded bootloader. In practice, once the firmware’s development has been completed, it will be possible not only to reprogram the ATmega via WiFi, but to make it by using the space usually reserved to the bootloader as well.

 

RTC module

Let us conclude the discussion about the circuit diagram with the RTC (Real Time Clock) module, composed of a classic Maxim’s DS1307, of a 32 kHz crystal, of a backup battery and of a pair of resistors on the

I²C line. The diagram is as classic as it gets, and is completely compatible with the existing Arduino libraries; all the functions are managed by means of the I²C line (SDA/SCL).

 

USB driver

Fishino MEGA uses an USB/Serial converter of the CH340G kind, which needs of specific drivers, at least for Windows (until version 7 included, it appears that starting from version 8 onwards the drivers are already found there) and for Mac systems. As for the Linux environment, on the other hand, the drivers are not needed since they are already found in the kernel. The drivers for Windows and Mac may be downloaded from the fishino_website’s download section.

Pages: 1 2 3 4 5 6 7 8

 


Top