It is a sheepskin with deep pile wool wrapped with latex balloons.

What, no styrofoam???

 

I'm working on a wooden table. Here is a portion of my circuit containing the NAND's. Obviously i'm using this circuit twice, and they are only connected to one another by utilising the same power source. The LTSpice circuit doesn't show the power source, but this is done as the same way as these inputs is, using a 7809.

The other major difference is that i'm using a BC548B in place of the BC847C (couldn't find a model of it, so used the next closest equivalent)

As I say, the circuit is working and doing what i want it to do, but ONLY on one circuit with the two NAND chips that are actually working...!? The other half wont work with another other chips, but will work with the two i have working, when i swap them over to that side.

 

It is a sheepskin with deep pile wool wrapped with latex balloons.

Then I see you are practicing good anti-static protocol.

 

Hey folks,

I'm working on a project which uses Texas Instruments CD4011BE NAND IC's. I'm finding a lot of them are going into the bucket due to them not working properly. I've been designing a circuit for the past couple of months, and have finished prototyping each component area of the overall circuit, and everything has been going well. Now however, i'm tryinig to get the main logic brain of my circuit working and have found that out of about 22 NAND chips i've bought, only 2 actually work in my circuit. I need four in total to work the whole thing. I've ordered another 16 from a seller on Ebay and i'm waiting for delivery later this week.

The two I have which work on one half of my circuit, i've moved between positions to the other half of the circuit, and have proven that they work wherever I put them. But as I say, these are TWO....of around 22! Out of the failing ones, I've resisted throwing about 10 of them straight into the bucket, and gone through the laborious exercise of testing them with a multi meter instead; testing each NAND gate in turn with all four permutations of input possible states. From this testing, I threw 4 away because I confirmed that, for whatever reason, one or more of the gates wasn't working properly. This left me with 6 (in addition to the 2 working ones) which tested fine with my multi meter testing, yet they still wont work with my circuit!? I'm most confused!!!??

Has anyone else had a great amount of difficulty with these chips? Am I destroying them with static even though i'm gingerly handling them with kid gloves, touching only the back plastic body?

any help/advice?

One of the first tricks I was taught in my career, was to hold static sensitive devices by the encapsulation and breathe on the pins just like you'd do before polishing spectacles. The condensation gently dissipates any static charge on the device.

In of itself; a static charge isn't what does the damage - its suddenly discharging it that does the mischief.

Most 4000 series chips have clamp diodes from the inputs to Vss and Vdd, but they can only stand about 10mA.

For things like semiconductor devices - Ebay can be pretty much the modern equivalent of the traders that used to sell mixed bags of factory seconds.

 

Is it possible that one of your inputs at power on is at 9 volts before the power supply for the IC's get their 9 volts?

 

Working...

V1 and V3 are at zero volts, so the output LED never will change.
There is no current limiting for the LED, which is ok in your case because its source voltage is 0 V.
There is no base current limiting resistor for Q3. This will cause the U1 to fail over time.
You can eliminate both double inverter strings, eliminating one entire 4011 device.
What is the function of the 7809 regulators in this circuit? Input conditioning?
If so, there are better ways for less cost unless you have a small barrel of them sitting around getting dusty (which, in fact, I do).

ak

 

Like say, they seem to work with a multi meter, at least the remaining ones i've not found a fault with and thrown in the bucket. they work under test ,but once i plug them into my circuit, they don't, even though the two "good ones" do work in the exact same positions!?

.

When I got started - there were still a lot of DTL chips in use (desk calculators).

It didn't take me long to discover that the high Ohms range of an AVO 8 could destroy the DTL input diodes.

Its not so easy to reverse bias the protection diodes on 4000 series, and modern DMMs are a little less brutal than an old analogue - but poking around logic chips with a multimeter isn't what most people do.

 

Some reading:
https://www.fairchildsemi.com/application-notes/AN/AN-375.pdf

 

There should be a resistor in series with the base of Q3, otherwise U1 is delivering it's (near) short-circuit current to Q1 (since the base-emitter junction looks like a diode) and that can damage U1 (but that may not be related to the problem you are are seeing).
You also need a resistor in series with D2 to limit its current. LEDs look like a forward-biased diode and need a current-limited source.
You need to read up on how to bias BJTs and LEDs.

 

Is it possible that one of your inputs at power on is at 9 volts before the power supply for the IC's get their 9 volts?

Another common error is when using a C/R to apply a pulse during power up. A diode from cap to Vdd must be used to discharge the cap when Vdd goes down at power off.

The 4000 series have a parasitic SCR in the structure of the inputs - normally they can't trigger unless a pin has residual voltage on it at power up.

An un clamped input capacitor will at best cause unpredictable operation - at worst; the SCR can crowbar Vdd and destroy the chip.

 

The circuit is to be put on to a car, so the MOSFETS are for limiting and controlling the operating power voltage and the inputs to the logic to a steady 9V.
I've built the circuit for real, and tweaked a few things here and there. For example, you reminded me, i have a 1k resistor after the logic but before the last transistor to energise the LED. I used to have a current limiting resistor in front of the LED, but because i'm using 12V automotive LED's which are designed to be applied straight to a car, i've found that i don't need a resistor in there, it just makes my LED dimmer.

When i mentioned using a multi meter to test my non funtioning NAND's, it was to take measurements to see that i was getting 9V out from a NAND when i was expecting it, and getting ZERO volts when both inputs were high.

As for the question of an input arriving before the VDD is high. I would find this unlikely, as they are all being powered using the same 12V power supply in my kitchen for prototyping. The circuit hasn't been anywhere near a car yet.

 

i think we might be getting off topic a little. My problem i suspect after conversation above, is dodgy chips. I'll see how the next batch go. My circuit can't be all that bad considering i've done considerable soak testing with the two working chips i have and they are still fine.

 

That's the correct function for NAND. Zero on any input gives 1 out; both 1 gives 0 out.

I'm aware of this. But i had chips which weren't sticking to the expect truth table results, and even had a couple which were giving me random voltages like 6V etc. weird.

 

I'm aware of this. But i had chips which weren't sticking to the expect truth table results, and even had a couple which were giving me random voltages like 6V etc. weird.

I deleted my post because I misread your post. You saw it before it got removed.

 

@Rissy,

Please send me a list of sellers that you purchase ICs from. I am very cautios when purchasing parts for the very reason that they may be fake or damaged. I have even had dodgy parts from reputable sellers!

Also here is something for everyone to have a chuckel on:

I purchased 50 555Ic's once from a reputable supplier on ebay. But what arrived was polysterine wrapped in foil with the parts pushed in. This would normally be OK if there is ALOT of thick foil but this was the thinnest foil you could find with only one wrap and half the pins where left unconnected. I had to throw them away because I could not risk one of these devices failing

 

I've bought the same chips from three sources.

i've bought 5 from Maplin, 2 of them on Saturday just past.
I've bought 2 from a seller on Ebay.
I've bought 16 from another seller on Ebay.

The problem is, i've lost track of which ones came from whom.

I've ordered another 16 from the last seller mentioned, and also another 2 from the first seller mentioned.

I don't know where the two that work, came from, unfortunately.

I'll be more careful with my next batches, and inform once I can report.

 

I purchased 50 555Ic's once from a reputable supplier on ebay. But what arrived was polysterine wrapped in foil with the parts pushed in.

I bought hundreds of components from an eBay seller who seemed to be buying in bulk and packaging in lower quantity at a price better than all on-line sources. I received dozens of CMOS ICs packaged in a polystyrene type material and put in regular zip lock bags.

When I complained, they explained that that's the way they had always packaged and I was the first to complain. eBay didn't have very good dispute system then, so I chalked it up as a learning experience...

 

...although, even once i CAN report, i'm sure i'll still be confused. Because as i said, although the other remaining chips wouldn't work on my circuit, they did mostly check out ok using a multimeter on some breadboard with 12V shoved up their arse.

 

The LED datasheet indicates that it does *not* have current limiting built in. This is consistent with automotive-type parts. I suspect that your 7809 is acting as a current limiter.

Looking at your circuit, it looks like a dual input OR gate, operating as an inverted input NAND gate, with an enable. Since V1 powers the LED, it seems redundant to have it a supply logic inputs. Is this correct?

ak

 

The LED is being driven directly from the 12V source (14V in LTSpice). the transistor simply opens up the ground path, allowing the current to flow, to allow the LED to illuminate.

The LTSpice LED is not what i have in real life. It's just the closest thing i could simulate with. I'm lighting up one of these...

http://www.ebay.co.uk/itm/151789701790?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT