I'm located near Chicago, the electronics stores nearby are a Micro Center and a store called American Science and Surplus, which has limited parts available, like a ECG153, ECG157, and a few other types of transistors.

Neither of those companies would be high on my list for purchasing electronic components.

You have a lot of mail order options: Jameco, Newark, Mouser, DigiKey. Until you've had time to build up some stock, you just need to plan ahead. When I buy components, I buy at least quantity 10 and usually buy at least 100 for better pricing per unit.

If you buy something in large quantity and want to trade them to get other parts you can use, there's a bartering thread in the Marketplace forum. I have hundreds of different components for trade.

There's always Amazon, which I'd like to avoid because parts can only be bought in bulk or for huge markups on single parts.

I'd stay away from Amazon, eBay, and AliExpress where the potential for counterfeits is a problem.

 

A teacher of mine (masters in electrical) said I should have them in parallel, what changes would having them in series make?

The more repeatable parameter for LEDs is the relationship between current and brightness. Thus, if you have a high enough system voltage, putting multiple LEDs in series with one current-limiting resistor will yield more consistent illumination, as opposed to LEDs in parallel with individual resistors. There is no one "right" way; different circuit and project conditions require different configurations.

Please post your schematic.

ak

 

A teacher of mine (masters in electrical) said I should have them in parallel, what changes would having them in series make?

Well if you only have 9v then you have no option. To have them in series requires 20 * Vf, where Vf is the forward voltage of the LED, say 1.2v for a Red LED, so 24v+ for 20 LEDs in series...

The correct way to fade an LED is to use pulse width modulation (PWM)_ You can then match the maximum brightness of each LED individually by adjusting its current by changing the resistor for each LED. Only then will each LED fade at the same rate.

 

Here's the current circuit, with added reference designators. As it stands, it works decently well.


I did initially consider PWM, but decided against it as I figured it would've made for too complicated a circuit for the parts I have on hand. This is also meant to be a small, potentially handheld build, so a huge voltage source would've been out of the question.

 

My "complicated" take on a PWM solution...

 

Here's the current circuit, with added reference designators. As it stands, it works decently well.

If you're happy, I'm happy.

ak

 

My "complicated" take on a PWM solution...

The issue is, I want the LED to be pulsing constantly without any human input. Plus, I don't have any MOSFETs. I looked at a few tutorials online, and the transistor / resistor / capacitor one looked the simplest and I already had all the parts on hand

 

The issue is, I want the LED to be pulsing constantly without any human input. Plus, I don't have any MOSFETs. I looked at a few tutorials online, and the transistor / resistor / capacitor one looked the simplest and I already had all the parts on hand

No human input needed... turn power on, it flashes LEDs. VR1 is a preset trimmer to allow manual speed adjustment, however the code could just as easily be written to be a fixed flash rate. The MOSFET is not essential, a suitable BJT, eg 2N2222, will work just as well since it's operating as a pure switch and not in its linear region.

I posted to show how few components are needed to meet the need digitally. This is often the case. I recently had a requirement to monitor 3 AC feeds to validate their presence and confirm their 'on' and 'off' sequences. After several days working with a bunch of opamps and 556 timers (dual 555) I finally ended up with 3 capacitors, 3 resistors and 3 AC input optocouplers and an ATtiny 8-pin MCU. 1/2 a day later I had a working solution for around $5, about 1/3 the price of the 'analog' answer.

If your solution works for you, thats great too!