This is a frequency counter question after reading Jeremy's neat code in http://www.picaxeforum.co.uk/showthread.php?t=5732&highlight=count+overflow
I'm designing a simple frequency counter for use to 200MHz, most for FM radio work. I've factored in a 1.1GHz MC12080 pre-scaler, and with the use of a second, or a divide-down-thru-5bits chips, can get the signal to a reasonable level where an 8, 16MHz picaxe could easily "count" it. A 64MHz 20X2 would be laughing.
The issue is, of course, the overflow. Only being able to count pulses up to 65535 means a bit of a loss of accuracy. You can shorten the gate, but you lose a bit of accuracy. You can divide down further, but same problem.
I'm trying to get a feeling for whether I could build on Jeremy's code for the 08M to run say, an 18X (vintage / classic!) with the 12080 pre-scalar and something like a 4040 to chop the signal down a bit further.
Aside from driving an LCD say 1x per second, the picaxe would be dedicated to counting. Auto-ranging might be nice but let's not get too fancy just yet! I could use a 4040 as the count coming out of pre-scaler is quite low - 200MHz / 80 = 2.7MHz which is accpetable for the (sluggish) 4040.
ANy advice appreciated. This will be built on a tighter-than-2-coats-of-paint PCB, ground plane on the other side, shielded cable.
I'm designing a simple frequency counter for use to 200MHz, most for FM radio work. I've factored in a 1.1GHz MC12080 pre-scaler, and with the use of a second, or a divide-down-thru-5bits chips, can get the signal to a reasonable level where an 8, 16MHz picaxe could easily "count" it. A 64MHz 20X2 would be laughing.
The issue is, of course, the overflow. Only being able to count pulses up to 65535 means a bit of a loss of accuracy. You can shorten the gate, but you lose a bit of accuracy. You can divide down further, but same problem.
I'm trying to get a feeling for whether I could build on Jeremy's code for the 08M to run say, an 18X (vintage / classic!) with the 12080 pre-scalar and something like a 4040 to chop the signal down a bit further.
Aside from driving an LCD say 1x per second, the picaxe would be dedicated to counting. Auto-ranging might be nice but let's not get too fancy just yet! I could use a 4040 as the count coming out of pre-scaler is quite low - 200MHz / 80 = 2.7MHz which is accpetable for the (sluggish) 4040.
ANy advice appreciated. This will be built on a tighter-than-2-coats-of-paint PCB, ground plane on the other side, shielded cable.