I built quite large numbers of a semi-smart battery charger that used the SMD 4541 timer to generate 14 hours on time. With a decent R and C in the oscillator, the end time never varied by more than +/- 3-4 minutes, or better than 1%. The divider chain lets you select divide by 256,1024,8192 or 65636, and it has a couple of neat control features, dirt cheap too, IIRC, about $1 each.
Barry Lennox
Well, you've got a lot of options:
And they show the list prices in their parametic charts, too.
Have Fun! Rich
There are sub-dollar parts (qty. 100) that can exceed your accuracy spec with no external parts (internal calibrated RC oscillator) and (most important) NO manual trimming or accuracy testing. By using an
8-pin part with an external resonator you could get 0.5% accuracy for about 65 cents (qty. 100)- eg. ATtiny11. You'd have a few I/Os left to play with, can add additional functionality cheaply, and the circuit will become more difficult to copy. Seems like a no-brainer. If the startup will pay you something for the couple of weeks it will take you to figure this stuff out (almost all learning curve), you'll both be ahead.Best regards, Spehro Pefhany
I second that.
construction. For
triode/pentode.
But an ECC 83 is a European 12AX7, which has a centre-tapped 12 volt filament.
In article , John Fields wrote: [....]
Use a thru hole film cap. After it is installed, cycle the whole PCB between the hot box and the freezer a few times befor you adjust the pot. The quick warm up and cool down work the stresses out of the parts and get the initial drift mostly over with before you tweek the pot.
If you do 90% of a resistor's value with a fixed resistor and the last 10 with a pot, you can reduce the tempco effects in the pot and make the tweeking easier.
The wiper connection is liable to become unreliable, so it's usually better to combine pots and fixed resistors in parallel, or better, series-parallel, to confine the adjustment range. Either way, the thing will still work at some level if the wiper opens.
Cheers,
Phil Hobbs
It depends on whether a little out of spec is better than completely stopped.
You could also use one of those EEProm based digital pots. In 555 like circuits, changing the effective voltage source for the resistor also can be used to trim the frequency.
What's the "wiper connection"?
A new spy novel title? Unless you post a quote of what you are referring to, it's hard to tell.
Don
The wiper is the metal bit wot touches the resistance element. There are actually two sliding contacts involved in most (not all) pots, a sliding low-resistance connnection to the moving contact and the wiper contact to the element. Good quality pots and trimpots are actually extremely reliable in most situations-- billions of them are made every year. In production situations it's nice to avoid the labo[u]r of adjusting them, but even that is a mixed blessing as much of the adjustment process can be an essential part of the test procedure.
Best regards, Spehro Pefhany
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