C-52 Evaluation Board 62256

A circuit diagram of the C-52 EVB is depicted in Figure 1. See at EA pinfirst, I put EA to Vcc configuring the 89C52 started internal code executionwhen reset. The first 8kB code space, 0000H-1FFFH is then be a monitorprogram, i.e., PAULMON2. A 32kB SRAM 62256 uses 15 lines address, A0-A14,while A15 of the 89C52 connects inverter gate, 74HC00, to CE pin. Thismakes the address space of the SRAM to be 8000H-FFFFH, i.e., A15 must be'1' to enable 62256. See OE pin, RD and PSEN are tied together with ANDgate made by two NAND gates. This makes the address space 8000H-FFFFH seenby 89C52 can be external code and data memory. Thus during in monitor modethat runs under PAULMON2, user may write hex code or download intel HEXfile to 62256. When jump from PAULMON2 to user program and run user program,this space is then be seen by 89C52 as a code space. Since P0 and P2 areused for connecting external RAM, left P1 and P3 for experimenting withreal world interfacing through input/output port. Nowadays there are manyperipheral chips that use serial protocol, say I2C, SPI. Thus only twoport is surely enough.

Multi-purpose dual power supply regulator board AMS1117

All embedded systems require electric power to operate. Most of the electronic components inside them, including the processors, can operate at a wide range of supply voltage. For example, the operating voltage range for the PIC16F1847 microcontroller is 2 to 5.5 V. But there are certain applications where you need a regulated constant voltage to avoid malfunctioning of the circuit or getting erroneous results. For instance, any application that involves analog-to-digital conversion (ADC) requires a fixed reference voltage to provide accurate digital count for input analog signal. If the reference voltage is not stable, the ADC output is meaningless. Here is my latest dual power supply regulator board that provides constant 3.3V and 5.0V outputs from an unregulated DC input (6.5-10V). It is small in size and can be easily enclosed inside the project box along with a project circuit board. It can also be used to power test circuits on breadboard. The board uses two AMS1117 series fixed voltage regulators and receives input power through a DC wall wart or an external 9V battery.

he regulator circuit uses two AMS1117 series fixed voltage regulators, AMS117 5.0 and AMS1117 3.3, to derive constant 5.0V and 3.3V outputs from an unregulated DC input voltage. The circuit diagram of the board is shown below.

Note that both AMS1117-3.3 and AMS1117-5.0 derive input power directly from the unregulated supply voltage, which means each of them can deliver up to 0.8A of current. However, for this particular board it is recommended to limit the output current up to 500 mA maximum. For the safety of the AMS1117-3.3 regulator IC, the unregulated input voltage is also recommended to be within 6.5 to 10.0 V. This board is best to use in a project that is designed tobe powered with a 9V DC from either a PP3 battery or a wall adapter. The PCB is only 1.9″ x 1.4″, and occupies a small area inside the project box.

 

The board doesn’t have any ON/OFF switch, because it may not be useful if this board is enclosed inside the project box. But through-hole pads are provided on the board if you want to add one externally. There are two surface mount pads which are shorted together by default with solder to close the circuit permanently. These must be disconnected if an external ON/OFF switch has to be added.

The regulated output voltages (5V and 3.3V) are accessed through screw terminal blocks. This power supply board can also be used to power breadboard circuits (see the picture below).