# Replacing A Sanyo Denki Fan Controller with a 555 timer

#### dredwinphd

Joined Aug 14, 2010
1
I was working on a design project which required some cooling fans. The fans I chose from Sanyo Denki have a sensor output which would can be used to feed the microcontroller with the fan information like the speed or whether the rotor has become locked.

I soon discovered that the signal from the sense line has to be conditioned. Sanyo Denki makes a small IC which, with a few resistors and caps, takes the sensor output from the fan and converts it to a micro compatible signal.

Now the catch, the IC is called a L8730 and no one stocks this IC and the minimum order is 100 pieces at $6.00 each. I would never use 100 pieces and the lead time for the device is almost six months. My question is would it be possible to use a CMOS 555 timer circuit to condition the signal? I am not a design wiz and wondered if someone would be interested in helping me figure this problem out? If anyone is interested in this little design challenge I can provide them with a copy of the L8730 datasheet and the fan datasheet. #### SgtWookie Joined Jul 17, 2007 22,210 Adding the L8730 and fan datasheets to the thread will be necessary for any progress to be made. Without them both, we can't even venture a guess whether your idea is viable. #### hgmjr Joined Jan 28, 2005 9,029 I was working on a design project which required some cooling fans. The fans I chose from Sanyo Denki have a sensor output which would can be used to feed the microcontroller with the fan information like the speed or whether the rotor has become locked. I soon discovered that the signal from the sense line has to be conditioned. Sanyo Denki makes a small IC which, with a few resistors and caps, takes the sensor output from the fan and converts it to a micro compatible signal. Now the catch, the IC is called a L8730 and no one stocks this IC and the minimum order is 100 pieces at$6.00 each. I would never use 100 pieces and the lead time for the device is almost six months.

My question is would it be possible to use a CMOS 555 timer circuit to condition the signal? I am not a design wiz and wondered if someone would be interested in helping me figure this problem out?

If anyone is interested in this little design challenge I can provide them with a copy of the L8730 datasheet and the fan datasheet.
Greetings dredwinphd,

My first impression of this problem is that you can forego the L8730 completely since the microcontroller possesses more than enough capability to implement the conditioning required. It was designed to be used in applications where there was no microcontroller present.

You will definitely need to provide a pull-up resistor to +5V assuming you are using +5V supply to power the microcontroller. This is because the output of the fan signal is an uncommited-collector or open-collector output. Most of these fan outputs consist of pulses that come at intervals the frequency of which is dependent on the speed of the fan. The signal amounts to a tachometer signal.

I don't know the level of your programming expertise. In this situation, I would feed this fan signal to an interrupt pin on the microcontroller. I would assign a bit to use to indicate that the fan was running. Inside the interrupt service routine this status bit would be set. In the main program loop I would test this bit and if set, I would clear it and start a timer. If the status bit stayed low and the timer reached the pre-determined value then it would be safe to assume that the fan had stopped rotating.

hgmjr