Frequency to Voltage Converter Help

[Jack Philpott]

For a recent school project, I came up with the idea of making a circuit which monitors bike pedal rpm (Cadence). Essentially spinning at an rpm of 90 will grow muscle that burns fat instead of short term energy.
The circuit I have designed is attached.
The input will be from an infrared phototransister that will pulse high each revolution.
I basically need to convert frequency into voltage which will then be used along side some comparators to turn some LEDs on that will be mounted on the handlebars. (I will probably also use a 3 to 8 decoder)
It will have to run on no more than 9v.
I know the circuit doesn't look pretty etc but I just need to get it functional first.
There are probably chips that will do all this for me but that would defeat the object of the project.
Help appreciated.

 

[Alec_t]

There are probably chips that will do all this for me

There are, but for a DIY circuit read up about f-to-v converters. That research will probably throw up references to monostable circuits. Once you have your voltage, read up about how you could use it with a LM3914 chip.

Edit:
I see from the attachment that you are already aware of monostable use.

 

[Herschel Peeler]

For a recent school project, I came up with the idea of making a circuit which monitors bike pedal rpm (Cadence). Essentially spinning at an rpm of 90 will grow muscle that burns fat instead of short term energy.
The circuit I have designed is attached.
The input will be from an infrared phototransister that will pulse high each revolution.
I basically need to convert frequency into voltage which will then be used along side some comparators to turn some LEDs on that will be mounted on the handlebars. (I will probably also use a 3 to 8 decoder)
It will have to run on no more than 9v.
I know the circuit doesn't look pretty etc but I just need to get it functional first.
There are probably chips that will do all this for me but that would defeat the object of the project.
Help appreciated.

What IC are you using for the comparator. You are looking for a high out. Some comparators are open collector and do not output a high. Pullup resistors are needed.