The part 3 of this series of posts covers the buying of Integrated Circuits at eBay. Naturally, this will only include some example ICs, since there are lots of different devices for sale there.
One important thing to highlight is that the price of the ICs is not necessarily the cheapest and, many times, we can find better prices at dedicated online stores. The common problem is that some of those stores only sell large quantities of devices or have a minimum shipping price that is considerably high for low quantities. On the contrary, at eBay, we can usually find single units or small packs of 5 or 10 ICs, and the shipping costs are typically small.
Other point to highlight is that there are some situations described around the web where people receive fake ICs. Personally, that has never occurred to me, but it’s a possibility that we need to consider when buying these devices at eBay. My advice is to only use eBay to buy small quantities of ICs for testing/prototyping and order them from dedicated and credited stores when going for large quantities.
Other than that, we should always select sellers with high numbers of sells and a positive feedback near 100%. Naturally, this consideration extends to any purchase at eBay.
The ULN2803A is an array of Darlington transistors, which is a configuration of two transistors that allow for a very high current amplification. This way, we can use this type of device, for example, to control a DC motor with a GPIO pin of a microcontroller without exceeding the current limit of that pin. This is exemplified in a previous post.
So, this is a very useful IC that a basic electronics kit should always have. Personally, I’ve use it in many projects and I always have a couple of them available.
The 74HC595 is a 8-bit serial-in parallel-out shift register that, amongst many other uses, allows to extend the number of digital pins of a microcontroller. With this useful IC, we can, for example, control multiple individual LEDs with only 3 pins of a microcontroller, as can be seen in this previous post.
The MCP4101 is 10 kΩ a digital potentiometer from Microchip, controllable via a SPI interface. It has 256 positions and can be used, for example, to control the intensity of the sound of a buzzer digitally using a microcontroller, instead of using a physically controllable potentiometer.
This IC is a little bit more expensive than the previous ones and can be bought at eBay for about 1.50 euros per unity, in DIP packages.
There are also digital potentiometers of 50 kΩ and 100 kΩ from this family of devices .