It’s Friday, my wife is off head-shrinking so I decided the first thing out of the box of goodies I just got from Digikey was going on the breadboard. Okay… so I lied to myself: a 74HC14… those are just restocking parts from a project I was working out that W2AEW had posted on his YouTube channel (the link is to the Youtube channel, if you’re not subscribed, you’re missing out.) So off to the next part.. A Microchip TC649 ?? What was that again? I don’t know about you but I just put random stuff that looks cool in my Digikey shopping cart until I am ready to place an order for stuff I actually need. Maybe I saw this in an Elektor article? Got me.. but hell PWM Fan Speed Controller with FanSense[TM]… neat! I downloaded the PDF to check it out; I was thankful I didn’t need to break out some i2c to get it running, it’ll run standalone with a thermistor. There is an example of using a microcontroller, I imagine I’ll use close to how their example design is shown. So, embarrassing, I know I have thermistors but I don’t know where they are? I used a 10k 10 turn pot. The Tc649 is looking for 2.7-1.8v No problem. I had a small fan so I used a 2N2222 and 810Ohm resistor for R_BASE. I recommend doing the math on the sense resistor (or it won’t pick up your stall) … They have a nice chart as well in the manual. I HIGHLY recommend sticking with 1uF for the PWM cap.. I played around with that, there is a reason they recommend it. In fact you’ll see my screen shots below are with a 0.47uF cap but the fan stalled while running faster than with 1uF. Not a lot more to say about this? It works! Very well in fact. The fan can just about be completely stalled with your finger (if you’re brave!) and it’ll continue to run… but you’ll be recycling power unless you build a reset into the circuit (I hadn’t). My circuit was running 5V, fan was on 12VDC (oh yeah, you can use “any fan voltage”) . I’ll hook this up to the first microcontroller to come out of the box later on this weekend! Until then.
Channel B: Pin 5 (Sense)
Channel B: Capacitor Cf (shown with 0.47uF) determines the frequency of of the PWM.
