After much searching, I have found a suplier who has a MAX 7219 display driver.
They also have 4 x 7-segment LED displays but I do not know which brand. Hoping that they are compatible.
My project is to use an optical sensor to measure RPM.
A large flywheel on the engine has 4 holes in it and I intend to use an LDR to sense the flashes of light as it rotates.
The sample input circuits show the LDR connected directly to the Picaxe with a resistor to ground. Should I do this or connect thru a flip-flop first ?
As there will be 4 pulses per rev. So will set the selector switch on the board to the 4 cylinder setting.
The display you are looking at probably will not work but I will post a new schematic for you that will work. You need 4 individual 7 segment displays. It is quite unlikely that the unit you found will be wired the same internally as the Lumex unit so look at the data sheets carefully. You also need very bright super red’s.
Unless you have a good reason, the LDR is probably not a good idea. You can derive a tach signal from any ignition source. If it is an engine it has one. There is a tach input link on the website also.
If you use the flip-flop you need to configure it as a divide by 2. Then the code will be for 2 cylinders as written.
If this is for a fixed application the dip switch to select cylinders isn't necessary. You can just set it in the code for the correct value. This removes the resistors and switch. You also need to #rem out the selection in the code and substitute you value there after the ADC read.
Here are two files you can view.
This is how to connect the MAX 7219 with the 4 individual displays. They are quire common, but check the data sheets to be sure they are pin-for-pin compatible with the LiteOn one I used or do a new schematic. They are also inexpensive so get 1 extra (for a mistake ..lol)... they must be CC.
MAX 7219 Connection
Here is a sheet I did for the race cars on the tach inputs:
Tach Circuits