Designing a digital watch from scratch ...

[smack Down]

Originally posted by: Bobthelost

Originally posted by: MrDudeMan
if you choose to use a battery, then fine it will be increasingly inaccurate, but why cant he make a rectifier and use wall power? it isnt going to magically heat up and cool off after it is turned on and stabilizes. once it reaches that state, nothing will vary and you no longer have to worry about 50+% variations like you claim.

Nice watch that would make

As if any one is going to use a bread board watch.

 

[MrDudeMan]

Originally posted by: Bobthelost

Originally posted by: MrDudeMan
if you choose to use a battery, then fine it will be increasingly inaccurate, but why cant he make a rectifier and use wall power? it isnt going to magically heat up and cool off after it is turned on and stabilizes. once it reaches that state, nothing will vary and you no longer have to worry about 50+% variations like you claim.

Nice watch that would make

lol, well i thought he was going for the experience in making one, not to actually wear a circuit board with a bunch of LEDs on it

 

[skimple]

Now that I think about it, I believe the ring oscillator was made with one inverter and then buffers to the desired delay length. Uses more gates, but you only get the transition once per period.

That's going back about six years, though...

 

[skimple]

Originally posted by: Navid

Originally posted by: skimple
I'm thinking VSLI circuitry, so all inverters would be on the same chip, and inverter to inverter variation would be minimal.

That is not going to help keep the frequency constant!

The frequency of the ring is a function of the absolute delay through the ring, which has nothing to do with the inverter-to-inverter variation.

I didn't mean that the variation would impact the total ring delay. I was commenting about the fact that by all gates being on the same chip, you would not have much variation between stages, so each stage would add an equal amount of delay. You couldn't do this with discretes. The variability between chips would be too big.

 

[Navid]

Originally posted by: skimple

Originally posted by: Navid

Originally posted by: skimple
I'm thinking VSLI circuitry, so all inverters would be on the same chip, and inverter to inverter variation would be minimal.

That is not going to help keep the frequency constant!

The frequency of the ring is a function of the absolute delay through the ring, which has nothing to do with the inverter-to-inverter variation.

I didn't mean that the variation would impact the total ring delay. I was commenting about the fact that by all gates being on the same chip, you would not have much variation between stages, so each stage would add an equal amount of delay. You couldn't do this with discretes. The variability between chips would be too big.

You are correct.

The variability of the delay between different stages of the ring affect the duty cycle of the oscillator output, which is irrelevant.

It is the frequency of the oscillator, and its accuracy and stability, that determines the accuracy and stability of the clock/watch.

You can have an accurate and stable frequency even if the duty cycle is not the same at different taps on the ring.

 

[BrownTown]

using a ring of invertors will get you a crazt fast speed, you want a lot lower frequency. Why cant yall just be satisfied with doing what a real watch does and have a crystal. After that its easy to wire the logic up. Just wire some counters up for each of the seconds/minutes/hours. Use some and gates and invertors to wire it so that when seconds = 60 you increment the minutes, and the same for hours. Then figure out the equations for the LEDs and used a Karnaugh map to create the optimized functions for each of the LED lights in the array. It should take like 10 minutes to create a block diagram given a constant input signal. And maybe 2 hours to generate the actual NAND gat combination to generate the display (i'm assuming youll be a real man and make it out of nothing but NAND gates). The only fly in the ointment is people arguing about using a crystal to generate the signal, but they are just over complcating things. If you want a 20 pound watch the stick on a transformer and Diodes onto the AC mains, but thats just stupid...