hippy
Ex-Staff (retired)
The diagram makes it clear and the 08M is redundant. The simple setup is as in the attachment.
There are two options for the pulse generation; let it free-run and synchronise to it ( as in attached ) or tell the generator to give a gating pulse when the counter is ready to start counting. That's probably better and easier to code.
On choice of crystal it doesn't really matter as long as you can generate a pulse of a length which makes the counter maths easy; 20ms = x 50, 25ms = x 40, 1000ms = x 1. The longer the better, the more accurate. Peculiar value crystals may cause a problem ( internal clock of 66.6666666ns etc ) but others, divided by powers of two may make things easier - 4.194304 MHz divided by 2^22 = 1s. If using a PICAXE to generate the pulse, the limited length of on-chip hardware dividers ( via counters ) is why a slower crystal is probably best.
There are two options for the pulse generation; let it free-run and synchronise to it ( as in attached ) or tell the generator to give a gating pulse when the counter is ready to start counting. That's probably better and easier to code.
On choice of crystal it doesn't really matter as long as you can generate a pulse of a length which makes the counter maths easy; 20ms = x 50, 25ms = x 40, 1000ms = x 1. The longer the better, the more accurate. Peculiar value crystals may cause a problem ( internal clock of 66.6666666ns etc ) but others, divided by powers of two may make things easier - 4.194304 MHz divided by 2^22 = 1s. If using a PICAXE to generate the pulse, the limited length of on-chip hardware dividers ( via counters ) is why a slower crystal is probably best.
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