Frequency Divider???

[MeAndYou]

Hello,

I’m trying to interface a “Speed Sensor” of a bike with a boost controller and I’m not too sure what I should use for my problem. What I need is a frequency divider. The frequency at the input trigger is continuously changing, since the pulses are in relation with the speed of the bike. I receive 687 pulses (as per the manual) at 60 KM/h (36 miles). I’m expecting that the relation between the pulses and the speed is linear. Did not have the chance to put the signal on a scope meter. The signal from the speed sensor is a square wave (High=5Vdc and Low=0Vdc). The speed of the bike is (0-320Km/h, 0-192 Mph). On the pin of the boost controller I have 5Vdc and I need to short that pin to the ground for that device to see a change.

The boost controller has a few ratios that can be chosen, but none of them give me an acceptable reading. So, I need a circuit that would tweak the ratio before it goes to the controller. I’ve looked at a LM555 and even if it says in the datasheet that it can be used as a frequency divider, I don’t see how it can work if the input signal is continuously changing. In a monostable configuration, the Output will stay high until the “temporization” is completed even if the input signal is retriggered many times during the temporization. It would work if the frequency of the input signal always stays the same, right?

Ok, what I’m looking for is a “Frequency Follower” circuit. This circuit would give me the possibility to adjust the ratio from 7 to 12 (potentiometer) with a transistor (NPN) that would act as a switch between the circuit and the boost controller to short the 5Vdc to the ground when the output goes High. I understand that there will be a delay in the response, but it is acceptable. Any ideas or ???? Thanks!!!

 

[Klaus]

How about a programmable, divide by n counter? 4018; 2 through 10 walking ring. You find circuits for that in the CMOS Cookbook.
Klaus

 

[Qema]

Sorry im not grasping what your trying to do but id like to help.

Are you tring to amplify the signal so that the peak of the wave form say 4 volts to 24 volts or do you want every 1 pulse to be changed into 4 pulses ?

 

[Roff]

Does your boost controller vary the boost as a function of pulse rate (RPM)? Are you saying you want a frequency divider whose division ratio can be varied? This is easily done, but using a potentiometer is probably not the easiest way to do it. Perhaps a rotary switch would be better.
Try to post as much info as you have - a copy of the specifications for this interface would be helpful.

 

[MeAndYou]

Thanks for all your answers!!!!

Klaus: I tried to find a link on the Internet for that book, but it seems that I need to buy it. I don’t think that binary counters would work, because the frequency will be divided by, 2, 4, 8, 16, etc… Am I wrong? That’s what I remember about binary counters. I need something that will permits me to divide the frequency by a “X” number, which I don’t know yet, but I have an approximate guess. Like I said it might be 7.2, 8.1, 9.4, or anything else.

Qema: I just want to change the frequency of the Input signal. Keep in mind that the frequency is continuously changing, since the pulses are proportional to the speed of the bike. What I want is a circuit that will divide the input frequency by a specific number at all time. After the correct ratio found, it will stay the same forever!!!

Ron: It sounds like that you know what I’m talking about! You are right the boost controller is dividing the RPM of the bike with the Speed. Whit the result, it can give the right amount of boost required. This is the boost controller that I’m working with:

**broken link removed**

This boost controller is to be used with a car and not a bike. The boost controller has a few ratios that can be chosen, but none of them give me an acceptable reading. It seems that the encoder of a car does not gives the same amount of pulses as the one mounted on a bike. So, the presets that can be selected in the boost controller (Japanese car, Nissan, Y32 Cima, etc…) are not good for me. That’s why a need to tweak the frequency that goes in the boost controller. I need to be able to adjust the ratio just for the initial tuning and after that I will not have to touch it anymore. The boost controller can display the speed of the bike. Right now the display on the bike does not match the display of the boost controller. With the circuit, I will be able to adjust the frequency and match both displays.

Any more solutions for me? Thanks!!!

MeAndYou

 

[Roff]

It will be difficult to divide by non-integer numbers (fractions). Are you sure you need to divide (as opposed to multiply)? If you are sure you need to divide, you need to specify a range of divisors before anyone can help you.

 

[MeAndYou]

Hi Ron,

Yes I need to divide. I already have an approximate ratio of 3 applied to the signal by the preset ratio of the boost controller. So when I have 687 pulses (60 Km/h) from the speed sensor, I get a reading of around 200 Km/h!!! As you can see, there is a little offset!

In my first post I said a ratio of 7 to 12, but this is something that I can find later by replacing a few resistors in the circuit or whatever is needed. If the input frequency would be fixed, I could use a LM555 with a potentiometer that would give me the ability to adjust the charge of the external capacitor (charge/discharge), which is used for the timing. But… this is not the case and that’s why I’ve posted my dilemma here, because I did not find any solution. Maybe there is no solution for me, but I think there must be something out there… I don’t want someone to design me the circuit, I just need someone to put me on a track that I don’t know.

Ron, thanks for your time and I don’t want to tie more of your time. Feel free to continue to help me out if you think you might have a piece of solution… Thanks!

Designing something to fix a problem is not always as easy as it seems.

Thanks to all of you. Keep posting if you think that you might have a solution!!!