digital circuit pg-46

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Volter
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digital circuit pg-46

Post by Volter »

I built the Digital Circuit, figure 11 on pg-46 but SET and RESET! One LED stays on while the other comes on at the push of button but that’s it!? What am I missing?
Thanks.
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evahle
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Digital Circuit

Post by evahle »

Hi Volter! I have the Nuts & Volts January 2009 issue in front of me now. I'm at page 46 and looking at Figures 10 and 11.

Did you mean you did or didn't have the Set and Reset buttons attached? Since you pressed a button, I assume you have them attached. Both must be attached for this to work. One button sets one LED on, the other off. The other button resets the first LED and turns the other back on again. This is a basic Flip-Flop Circuit.

Lets start with the basics:

1) Look at Fig 11 on the bottom right corner. The 2 resistors that aren't marked, are 1 k resistors. In the middle upper of fig. 11 are the transistors. The left one is Q1 and the right one is Q2. I would mark these on the page for future reference.

2) With a voltmeter, we need to verify all the basic voltages. Place the black(negative) probe on the ground part of the battery.

3) In fig. 11, follow the wire from the positive side of the battery, to pin j of L1(LED1) and to the jumper wire. With your Red(positive) probe, measure the voltage there. It should read the battery voltage(about +9v). If not, recheck your wiring to that point. As you can see, this also connects to the two 1k resistors. Check for +9v there too. If you look at fig.10 (the schematic),you'll see the +9v only connects to the two 1k resistors, so that is the only thing we need to check for the +9v.

4) Remove the Black probe and place the Red probe on the positive side of the battery. We'll check for all the ground points next.

5) Follow the ground wire from the battery in fig.11, and you can see that it connects to the Emitter of transistor Q1. Place your Black probe there. You should read +9v (because your black probe is connected to ground now). If not, recheck your wiring to that point.

6) Next follow the wire from Q1 emitter, to Q2 emitter and place the Black probe on the emitter of Q2. Again, you should read +9v.

7) Follow the wire from Q2 emitter to pin j of S3, and the jumper there. You'll also see that this connection also connects to S4. Place you Black probe on each of these points and you should read +9v.

If all of these basic voltage checks are ok, then the only thing left are the Collectors and Bases of each transistor to check. I don't know how much you know about these tests, but I've included them in case someone doesn't know how.

Usually we assume when something doesn't work from soemone else's schematic, that the schematic has an error, but I see none here, other than the missing labels.

If the previous tests are ok, then we can continue testing the operation of the Flip-Flop. Let me know.

hope this helps
evahle :smile:
Bigglez
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Re: digital circuit pg-46

Post by Bigglez »

Volter wrote:I built the Digital Circuit, figure 11 on pg-46 but SET and RESET! One LED stays on while the other comes on at the push of button but that’s it!? What am I missing?
Do you have the jumpers ("jmp") installed on your Proto Buddy?
Volter
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Post by Volter »

I found the problem. It is the PCB trace layout that involves the jumper part. Instead the jumper going from S3-j to S4-j it jumps directly to S4. I hope this description helps or if you accept JPG or GIF image I can send you that. :eek:
I can retrace that, luckily it is at the bottom so no one will see.
Thanks. :cool:
Volter
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Post by Volter »

So, it is the drawing that does not mach the PCB! I finally unwired it and found out that the S4 terminals are switched. If would I notice that right away I could switch just one wire but since I took the wires off I had to reconnect all, that’s fine, it works now. :grin:
Thanks!
Bigglez
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Post by Bigglez »

Volter wrote: I found the problem. It is the PCB trace layout that involves the jumper part. Instead the jumper going from S3-j to S4-j it jumps directly to S4. I hope this description helps or if you accept JPG or GIF image I can send you that.
Perhaps a diagram will help me understand. Anyone can attach
an image to their posts on this forum.
Volter wrote: I can retrace that, luckily it is at the bottom so no one will see.
Retrace? Bottom? I'm confused....
Bigglez
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Post by Bigglez »

Volter wrote: So, it is the drawing that does not mach the PCB!
I don't see a PCB diagram in the article, where are you looking?
Volter wrote:I finally unwired it and found out that the S4 terminals are switched.
In the print article? A download? Or, just your version?
Bigglez
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Post by Bigglez »

Bigglez wrote:
Volter wrote: So, it is the drawing that does not mach the PCB!
I don't see a PCB diagram in the article, where are you looking?
Volter wrote:I finally unwired it and found out that the S4 terminals are switched.
In the print article? A download? Or, just your version?
Okay, I think I see it now. Check out Figure 5, page 45.
The sequence of connections from L to R are:
S1 S1, S2 S2, TB1 TB2 TB3, S3 S3j, S4 S4j, etc.

In the diagram below it (Figure 6, page 45) the sequence
of connections from L to R are:
S1 S1, S2 S2, TB1 TB2 TB3, S3 S3j, S4j S4, etc.

As you said, S4 is switched. Hmm... No one else caught it!

Does your flip-flop with LEDs work correctly now?
Volter
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Post by Volter »

Yes, it works now. At first I thought it might be the resistance that I got, the 2 100Kohm might cause the issue since I had to put some R in series getting 90K and 94K since I did not have any 100Ks but it should handle some tolerance for my purpose.
Too bad I did not know what other circuits you might present and so I do not have the Schotky NANDs and MOSFETs so that will have to wait a bit until I get those.
Anyway, thanks for the troubleshooting hints and also, would you have any suggestions on what kind of supply of components would be good to have on hand? They do not cost that much and making a large order would be better then buying 1 or 2 at a time.
Thanks much.
:cool:
Bigglez
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Post by Bigglez »

Volter wrote: Yes, it works now. At first I thought it might be the resistance that I got, the 2 100Kohm might cause the issue since I had to put some R in series getting 90K and 94K since I did not have any 100Ks but it should handle some tolerance for my purpose.
The flip-flop circuit is inherently symmetrical. At power
up it relies on one transistor's gain being greater, and
in a race one transistor will conduct, robbing the other.
This is a random event. If both transistors were
identical the circuit could power up as both transistors
conducting!

The tolerance on the hFE of the trnasistors (100 - 300 at
10mA, as defined by the LED resistors) is very wide, much
wider than the resistors (5% - 10% total).
Volter wrote:Too bad I did not know what other circuits you might present and so I do not have the Schotky NANDs and MOSFETs so that will have to wait a bit until I get those.
You have lost me again.
Volter wrote:suggestions on what kind of supply of components would be good to have on hand? They do not cost that much and making a large order would be better then buying 1 or 2 at a time.
A lot depends upon what you like to experiment with.
For basic circuits you should have a set of 1/4W 5%
(or 1%) resistors in every standard value from 10R
to 10M, some values are more common, so stock
these (100R, 470R, 1k0, 4k7, 10k, 47k, 100k, 1M0).
Same for capacitors, although small electrolytics in
4u7, 10u, 47, 100u will do. Non-electrolytics in
10n, 47n, 100n will do. I seldom use vlaues outside
that range on a SBB.

Small signal NPN and PNP transistors (2N3904, 3N3906
or 2N4401, 2N4403). Some small signal FETs (2N7001
or similar).

Fixed voltage linear regulators ('78L05, 7805).
Some 3mm amd 5mm coloured LEDs, possibly
a few seven segment or 14 segment LED displays.

For analog circuits some Op amps like LM741,
LM1458 (dual), LM324 (quad).

For digital circuits some basic gates and latches
in CMOS (4000 series) or TTL compatible CMOS
(74HC*** - there are many varieties with the
same logic function). NAND and NOR gates are
most versatile).

Fifty bucks spend wisely at DigiKey or Mouser
would bring enough branded and tested parts to
build literally hundreds of SSB experiments.

Many commondity parts will also show up for less
money on auction sites (eBay).
Volter
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Post by Volter »

Too bad I did not know what other circuits you might present and so I do not have the Schotky NANDs and MOSFETs so that will have to wait a bit until I get those.
When I got the parts for the project there were no CD4093, Cap 1uF, and transistor 2N700 as it shows in the parts list in the January issue.
Thanks.
Bigglez
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Post by Bigglez »

Volter wrote:When I got the parts for the project there were no CD4093, Cap 1uF, and transistor 2N700 as it shows in the parts list in the January issue.
I answered your question about buying parts for a hobby,
how is this related to the N and V magazine article?
Volter
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Post by Volter »

Because you know so much!!! You knew where I came from the first time and this site IS about N and V!
Bigglez
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Post by Bigglez »

Volter wrote:Because you know so much!!! You knew where I came from the first time and this site IS about N and V!
Thanks for the kind words! Sadly, few posters here
read the magazine, even fewer contribute to it.
Volter
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Post by Volter »

Judging from the content I am surprised to hear that there are not too many involved! Nuts and Volts is one of the “BESTâ€
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