SRAM is a type of memory that will store information, but lose it when power is disconnected, which is why it is RAM. It is called static RAM because it doesn't need to be refreshed, unlike Dynamic RAM (DRAM) which has to be refreshed every few milliseconds to keep its data. DRAM is common in computer memory, because of fast access times and it only requires 1 transistor and 1 capacitor per bit making it high density. SRAM is common among microcontroller memory and some low power applications because it doesn't need to be refreshed, and uses less power. It is slower than DRAM and has a lower density at 6 transistors per cell.
This instructable will show you how you can make a SRAM bit using the real design, not the register versions I previously demonstrated. The SRAM is the 6t circuit, meaning that this version uses 6 transistors per bit (in reality, ours will need 8 per bit).
Why build such a device, when you can get an IC with a few thousand times more storage?
Because its cool to see how those little chips actually work. Plus you can say that you made your own RAM... and maybe tell all your friends that your computer is running off of homemade RAM...
Step 1: Get The Stuff
- 8 2N7000 transistors - These are N-channel MOSFETs
- 4 BS250 transistors - These are P-channel MOSFETs
- 1 LED
- 1 Resistor to match LED current - 220 - 1K will be fine. http://led.linear1.org/1led.wiz is a good calculator if you aren't sure
- 2 Buttons
- 2 Resistors 1k to 10k will work
- A breadboard
- A 5-ish Volt Power Supply