RESET circuit tweaks

Post by **Icky** » 10 Nov 2018 20:04

Forgottenmyname wrote: 10 Nov 2018 20:01
Icky wrote: 10 Nov 2018 19:59

Must of seen the same thing at the same time :D
470 and original is the 10

So by my calculation thats 480uF assuming those numbers are uF.

Post by **PhilC** » 10 Nov 2018 20:05

Yes 480uf as both are in parallel.

PaulJ · Post by **PaulJ** » 10 Nov 2018 20:07

Icky wrote: 10 Nov 2018 19:58
Forgottenmyname wrote: 10 Nov 2018 19:51 If it helps, here's a photo of my Mega reset circuit, in case something is a different value to the schematic.

20181110_194921.jpg
Thanks Forgottenmyname - I notice your C3 is two caps in parallel. What value are they?

No double cap here. Its a 10 uf

.

IMG_2073.JPG

PaulJ · Post by **PaulJ** » 10 Nov 2018 20:14

Does the second cap look factory or a user hack?

Post by **Icky** » 10 Nov 2018 20:14

Just tried 470uF in parallel.

Its weird. Its just doesn't seem to be behaving as expected. Reset switch doesn't affect anything. Have checked and checked the circuit. I have two TL7705's so both of them cant be duff.

Post by **PhilC** » 10 Nov 2018 20:18

Just looking at the data sheet at the mo, the difference in CT will mean a longer reset delay if I am reading this correct, so just means a different delay. Maybe one of my Mega's is a little slow at starting and needed encouragement?

Post by **Icky** » 10 Nov 2018 20:18

Icky wrote: 10 Nov 2018 20:14 Just tried 470uF in parallel.

Its weird. Its just doesn't seem to be behaving as expected. Reset switch doesn't affect anything. Have checked and checked the circuit. I have two TL7705's so both of them cant be duff.

And now its gone back to the occasional bouncing inverted reset out after powering on again.

Post by **PhilC** » 10 Nov 2018 20:27

Being thick today but comparing schematics, mega values for C1 and C is .1uf but we are using 10nf.

Also bizarrely, the data sheet for the 7705 shows ref connected to VCC but on the mega drawing and the reset board it goes to gnd via a cap.

data sheet if useful

http://www.ti.com/lit/ds/symlink/tl7705b.pdf

Post by **Icky** » 10 Nov 2018 20:30

Forgottenmyname wrote: 10 Nov 2018 20:27 Being thick today but comparing schematics, mega values for C1 and C is .1uf but we are using 10nf.

Also bizarrely, the data sheet for the 7705 shows ref connected to VCC but on the mega drawing and the reset board it goes to gnd via a cap.

data sheet if useful

http://www.ti.com/lit/ds/symlink/tl7705b.pdf

Interesting spot. I just powered on the prototype circuit again and it seemed to work with pulses.

Screen Shot 2018-11-10 at 20.27.15.png

Post by **Icky** » 10 Nov 2018 20:43

Icky wrote: 10 Nov 2018 20:30
Forgottenmyname wrote: 10 Nov 2018 20:27 Being thick today but comparing schematics, mega values for C1 and C is .1uf but we are using 10nf.

Also bizarrely, the data sheet for the 7705 shows ref connected to VCC but on the mega drawing and the reset board it goes to gnd via a cap.

data sheet if useful

http://www.ti.com/lit/ds/symlink/tl7705b.pdf
Interesting spot. I just powered on the prototype circuit again and it seemed to work with pulses.

Screen Shot 2018-11-10 at 20.27.15.png

And now its back to no activity on inverted Reset. :headbang:

RESET circuit tweaks

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