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Re: General Stuff(tm)
Posted: 19 Dec 2021 22:16
by stephen_usher
It's really frustrating waiting for components.
The 555s and 556 chips are sitting in Stansted Airport and have been for nearly a day.
I've pretty well proved that it's the first timer in the 556. The Threshold input is pulling the Discharge line down to ~2.5V. Lift the pin and the D line will bounce up to the correct 5V. The Threshold just goes to a comparitor and hence shouldn't draw much power at all.
Re: General Stuff(tm)
Posted: 19 Dec 2021 22:18
by derkom
stephen_usher wrote: 19 Dec 2021 22:16
The 555s and 556 chips are sitting in Stanstead Airport and have been for nearly a day.
Sounds quite similar to my most recent experience at Stansted.
Re: General Stuff(tm)
Posted: 19 Dec 2021 23:05
by rubber_jonnie
stephen_usher wrote: 19 Dec 2021 22:16
It's really frustrating waiting for components.
The 555s and 556 chips are sitting in Stansted Airport and have been for nearly a day.
I've pretty well proved that it's the first timer in the 556. The Threshold input is pulling the Discharge line down to ~2.5V. Lift the pin and the D line will bounce up to the correct 5V. The Threshold just goes to a comparitor and hence shouldn't draw much power at all.
Before we were bought out, our office was at Stansted, we had a grandstand view when Trump arrived!
Re: General Stuff(tm)
Posted: 20 Dec 2021 07:33
by stephen_usher
Good news: The chips have arrived at the delivery depot.
Bad news: They're not going out for delivery until tomorrow.
Re: General Stuff(tm)
Posted: 20 Dec 2021 08:51
by rubber_jonnie
stephen_usher wrote: 20 Dec 2021 07:33
Good news: The chips have arrived at the delivery depot.
Bad news: They're not going out for delivery until tomorrow.
How very annoying!
Don't they know that some of us are looking forward to the next stage of this story!!
Re: General Stuff(tm)
Posted: 20 Dec 2021 09:11
by stephen_usher
:lol:
Re: General Stuff(tm)
Posted: 20 Dec 2021 09:47
by stephen_usher
Oh, looks like the e-mail lied! :-)
Screenshot_20211220_094607.jpeg
Re: General Stuff(tm)
Posted: 20 Dec 2021 10:55
by stephen_usher
I haz chips!
:cheer: :cheer: :cheer: :cheer:
Re: General Stuff(tm)
Posted: 20 Dec 2021 18:34
by stephen_usher
Well, the new chip hasn't fixed things. I do at least have a serial clock now but for some reason the drain on the first 555 is constantly triggered and CV is a weird voltage. *sigh*
P.S. OK, this means that it's not being triggered, even though the signal coming in does seem to be going below 1/3rd Vcc. Going down to 1.2V with Vcc 4.72V)
P.P.S. Looking at the TI data sheet, the V-Trig voltage for the NE556N at 5V Vcc is typically 1.62V... *BUT* can be as low as 1.1V. So, with a Vcc of 4.72V this could be even lower with certain batches of chips.
Re: General Stuff(tm)
Posted: 20 Dec 2021 19:18
by stephen_usher
OK, theory confirmed. Putting a 10K resistor between GND and the data in pin (pulling the mean voltage of the data line to 2.5V, balancing the 10K pull-up allows the data pulses to go low enough to trigger the 555. So, I'm going to have to fit that on the back of the board.