E/16/231 Sawan Mapalagama
EE356 Electronic Product Design and Manufacture
Adding SPI Flash Memory for the Temperature Logger
When we are looking at the customer requirements, it we should design a
temperature logger which could obtained 100,000 data.
Let’s have a calculation to identify how much of memory space that we need to
obtain this.
for 100,000
when the date and time of each temperature could store by using epoch
timestamp,
So, time could represent as a number and that number would be 4byte.
And the Temperature can be represented as a number and it is also a 4byte data.
So, one data will be overall, 8byte.
Therefore for 100,000 samples,
it should be 800,000byte
it means 800,000b/1024 = 781.25kbyte
so, we should have at least 1Mbyte memory space for our logger
then we can store it with,
each data may count in 15mins of time intervals
Those data could be updated to a table, which has two columns.
as a 100,000 x 2 matrix.
By looking at the above calculations,
I have found a SPI Flash which called MX25V8035F
And It has a 8Mb space and it can be powered by 3.3V and the supplies device
package is 8-SOP.
https://media.digikey.com/pdf/Data%20Sheets/Macronix/MX25V8035F.pdf
Figure 01: SPI flash Memory and Microcontroller
Figure 02: Completed Schematic Diagram
Figure 03: Pin Diagram of MX25V1006F
Pin connection
As shown in Figure 03, there are 4 pins should connect to the Microcontroller. Those
Microcontroller and the SPI Flash are working as a master and a slave architecture,
the SPI Flash is the slave component.
So, SI (Slave Input) and SO (Slave output) should connect appropriate pins in the
microcontroller,
Other than that, SCLK which represent the clock of a microcontroller should connect
and the CS# pin which represent the Chip Selector should connect properly. When it
is negative value in CS# it is good to has pull up resister with 10k value.
VCC should connect to the power with the 10nF decoupling capacitor. WP# and
HOLD# should be kept on pull up position.
Problem I faced
1. There were a calculation to do to find out the necessary memory chip.
2. Initially the LEDs were allocated to the PA4 and PA5 pins. But when the SPI Flash is
adding to the circuit, the dedicated pins had to connected to the SPI Flash. So, the
LEDs were shifted to the free pins while SPI flash connected to the relevant pins.
3. The connections of negative pins should have a pull up resistors.
4. The power (VDC) need to has a decoupling capacitor If the input voltage drops,
then a decoupling capacitor will be able to provide enough power to an IC to keep
the voltage stable.