Please help with "Voltage divider with capacitor circuit" from Keith Brindley's "Starting electronic 3rd Ed"

ASSuMEing that everyone (or, indeed, ANYone) has that book is quite an imposition on the group.

The way to get good help is to put up a copy of the *schematic* here so that EVERYONE can see it.

One way (the easy way) to do that is

2) Upload that image to a "image hosting service".

You MUST use software that allows a monospaced font (like Courier). e.g. The Kate text editor will do this. This software makes this even easier:

If you attempt to do this in Google's font rather than cut & paste from non-proportional font editor the results will be a complete mess.

(When you paste it into Google it will appear a mess to you. It won't to those using a real Usenet newsreader.)

I didn't know of some of these tools, thanks.

The following ASCII can be cut n pasted into a new file and loaded into LTspiceIV, it's probably not the neatest, but I couldn't find a way of rearranging the pins on the 555.

Thanks, Luke.

--- divider.asc ---

Version 4

SHEET 1 880 680

WIRE -160 -96 -336 -96

WIRE 16 -96 -160 -96

WIRE 384 -96 16 -96

WIRE -160 16 -160 -16

WIRE 352 16 -160 16

WIRE -160 64 -160 16

WIRE 112 64 48 64

WIRE 384 64 384 -96

WIRE 384 64 336 64

WIRE -336 96 -336 -96

WIRE 112 128 0 128

WIRE 352 128 352 16

WIRE 352 128 336 128

WIRE -160 176 -160 144

WIRE -32 176 -160 176

WIRE 112 192 80 192

WIRE 416 192 336 192

WIRE -160 208 -160 176

WIRE 0 208 0 128

WIRE 0 208 -160 208

WIRE -160 240 -160 208

WIRE 16 256 16 -96

WIRE 112 256 16 256

WIRE -32 320 -32 176

WIRE 416 320 416 192

WIRE 416 320 -32 320

WIRE -336 432 -336 176

WIRE -160 432 -160 304

WIRE -160 432 -336 432

WIRE -64 432 -160 432

WIRE 80 480 80 192

WIRE 80 560 80 544

WIRE 288 560 80 560

WIRE 80 576 80 560

WIRE -64 672 -64 432

WIRE 48 672 48 64

WIRE 48 672 -64 672

WIRE 80 672 80 656

WIRE 80 672 48 672

WIRE 288 672 80 672

SYMBOL Misc\\\\NE555 224 160 R0

SYMATTR InstName U1

SYMBOL res -176 -112 R0

SYMATTR InstName R1

SYMATTR Value 4k7

SYMBOL res -176 48 R0

SYMATTR InstName R2

SYMATTR Value 10k

SYMBOL res 64 560 R0

SYMATTR InstName R3

SYMATTR Value 1k5

SYMBOL cap -176 240 R0

SYMATTR InstName C1

SYMBOL cap 64 480 R0

SYMATTR InstName C2

SYMATTR Value 100n

SYMBOL Misc\\\\battery -336 80 R0

SYMATTR InstName V1

SYMATTR Value 9V

TEXT 288 608 Left 0 ;Multimeter to read 50V (AC)

You didn't include a ground on the schematic and LTSpice kind of wants that placed somewhere in order to simulate it.

As you have it, C1 participates in setting the period. You didn't specify a value on the schematic, so I just used 10uF as a default. C2 modifies the tau (duration) of the pulse you observe on an oscilloscope. If you are using a multimeter, though, you are probably going to have a hard time observing it unless C2 is pretty large and even then you will "observe" some kind of averaging, probably. Do you have a scope or logic analyzer of some kind to use? That may help a lot with looking at the results of what you are building.

Jon

Well, I'll look into that :D

C1 is switched between 10 microF, 1 microF, 100 nF, 10 nF and 1 nF. In his results, he gets 0V, 0V, 1.5V, 4V and 4.2V respectively, this is when C2 =3D 100 nF. I match these results except for the last one where I get something like 0.14V. My multimeter is set to 20V AC range.

Also, when C2 is 10 nF, he gets: 0V, 0V, 0V, 1.5V and 4V for the above, again, my last reading doesn't match.

Nope, just a DMM.

Thanks, Luke.

Hi Luke,

if you plot the FFT of your output voltage with your LTspice, you'll see that with C1=3D10n, the output frequency is about 5.8kHz but if you change the C1=3D1n, the FFT will show your output frequency is about 57.4k Hz. most of the DMMs will have a AC frequency measuring range. some 30kHz even less. so there is high probability that you DMM is not rated for that high frequency measurement. check the spec on that. it's best to use a oscilloscope or analyzer for this type of measurement.

hope it helps.

yours Ren

AC Current Frequency range: 50Hz to 500Hz

Capacitance Test Frequency: 2 dot 5 (where dot is a full stop in the middle vertically, not like a decimal point)Hz Models PG012 & PG017

Frequency Ranges (autoranging): Model PG017 - 2kHz to 15MHz

Mine is a PG017.

Well, if that explains why I'm getting different results for that one capacitor, then yeah it does, thanks :D

Luke.