Barracuda Legend Kit Problems

[Qiaozhi]

I'm not sure which version of the Baracuda schematic you are all looking at, but it would appear that the CD40106 should have its VCC pin connected to GND, and its VSS pin connected to -5V.
The reason being that the 2N5485 sample gates are N-channel JFETs. This means that when the JFET is conducting (on) the gate has 0V applied, and is off when the gate is in reverse bias (i.e. at -5V).
Basically, the original circuit looks ok to me.

[FatBob]

Ok but is it right to connect the timing resistors to +5 with the chip at Gnd and -5V?

[ODM]

If it's been built wrong, then all bets are off. Was just pointing out that this is not a nice way to treat logic ICs. It's an old schematic and it was most likely a noticeable saving in parts and assembly to omit voltage underswing protection. Low current outputs are a blessing in this sense.

Where was the scope common connected in the above picture, raydgunn?

[raygdunn]

If it's been built wrong, then all bets are off. Was just pointing out that this is not a nice way to treat logic ICs. It's an old schematic and it was most likely a noticeable saving in parts and assembly to omit voltage underswing protection. Low current outputs are a blessing in this sense.

Where was the scope common connected in the above picture, raydgunn?

Clipped to the protection diode on B+. I'm using the "median" setting on both signals to improve the vertical positioning, so one can't directly compare the signals. But I'm guessing that is a usual setting.

Ray

[Impulse]

Hey guys i have my pc back to full health yay! so i can continue with the barracuda build, in the mean time i have made a coil with 0.5mm enamelled wire 14 turns wrapped with 1mm plastic spiral wrap and a mesh sheild taped on with paper tape, OK! so i have tried the coil and the movement issue is 90% gone but the coil is so slow i may as well just dig random holes at the beach with my son i will have better luck! but it is a step in the rite direction .

what wire would you sugest i buy? i have found this?

http://www.ebay.co.uk/itm/4008140503...%3AMEBIDX%3AIT

any good? or junk?

[Old cart]

Well I do not wish to argue here. I just want to say if you put a resistor to 10V between 2 caps the voltage (between the caps) will rise to 10v.

[ATTACH]35544[/ATTACH]

The power pin of the 40106 must be at the highest potential of the circuit (IE 20v , +5V).

I believe this is the way it should have been done;

[ATTACH]35545[/ATTACH]

I see what you are saying. The spec sheet says the inputs should never be higher than the highest supply pin plus .5 volt. In this case that is ground so in your fixed schematic your connection to plus 5 IS ground and it should work fine and not violate ratings. Clearly the way this is designed violates that. You solution should fix that problem. The fact that the design works is merely a testimony to the fact that some brands or indivual chips can survive this abuse. I do not believe violating absolute max ratings is ever a good idea though.

[Old cart]

Hey guys i have my pc back to full health yay! so i can continue with the barracuda build, in the mean time i have made a coil with 0.5mm enamelled wire 14 turns wrapped with 1mm plastic spiral wrap and a mesh sheild taped on with paper tape, OK! so i have tried the coil and the movement issue is 90% gone but the coil is so slow i may as well just dig random holes at the beach with my son i will have better luck! but it is a step in the rite direction .

what wire would you sugest i buy? i have found this?

http://www.ebay.co.uk/itm/4008140503...%3AMEBIDX%3AIT

any good? or junk?

Does your shield have a gap in it so there is not a complete ring or closed loop around the coil? What kind of shielding are you using? As for wire that should be fine. It may not be as fast as more exotic solutions but it should be fast enough since coil speed is primarily driven by interwinding capacitance which is primarily determined by the spacing between each turn of the winding and also by the spacing between each turn and the shield. In your case you might try to layer two layers of the spiral wrap around the coil and apply the shield on the a outside of that being very careful to leave a gap of maybe 8mm between the ends of the shield.
Did you ever try the single shorted loop of wire experiment I described earlier?

[Old cart]

It shows a 5V supply for the 40106 but some of the timing resistors tie to 5V above
the positive pin!
--
yup. and what??? you want to say that is wrong?

Yes that is wrong. See the absolute maximum ratings for the 40106 input voltage.
http://www.ti.com/lit/ds/symlink/cd40106b-mil.pdf

This is the TI B version of the chip.

The inputs can never go above .5volts in the Baracuda or this spec is violated. Since the input impedance is high the resistor in series drops essential no voltage. Depending on the protection diode this voltage could be .7 volts or higher. In this thread alone we have seen at least two damaged 40106 problems. This could well be the reason, or it could be simple static damage.

[Old cart]

your schematic is BBBAAADDD.... DELETE IT AND FORGET. (i had deleted all those schematics drawn by Alex - much mistakes).
[ATTACH]35162[/ATTACH]

Actually on this schematic the resistors connect to Vdd, which is 0 volts on the Barracuda. So the board looks wrong!

[Old cart]

your schematic is BBBAAADDD.... DELETE IT AND FORGET. (i had deleted all those schematics drawn by Alex - much mistakes).
[ATTACH]35162[/ATTACH]

Ok i have taken readings from the 40106 and pin 1,0.55v 2,4.9v 3,0.48v 4,-4.8v 5,0.16v 6,-4.7v 7, -4.9v and pin 14, 0v. i have borrowed an o-scope but it will not turn on atm batt is flat across the coil and 8.3v AC 0.22v DC and now the board does not function at all nothing not a beep unless i pull the power off it and i get a whine as the power drains, nothing changed ?

Here is a good example. Impulse has .55 volts on pin 1 of the 40106. This is an actual measured voltage, not a simulation. This clearly exceeds the absolute maximum input voltage rating of TI. This 40106 also is not working correctly. It introduces additional pulses that should not be there. They are runt pulses ( smaller than normal) the occur on the rising and falling edges of the transmit pulse. These may have no effect on the Baracuda operation, but they should not be there!

One simple solution would be to cut the trace that leads to the +5 volt regulator very near the 33k resistor attached to pin 1 of the 40106. Cut the trace between the 33k and the regulator NOT between the 33k and pin 1. This will allow R17,18, and 19 to float. Then tie this point to pin 14 of the 40106 with a thin jumper wire. This hold place pins 1 ,3 and 5 at 0 volts which is still a logic high and will not exceed the chip specs. However it will likely alter the timing of the two timing pulse and require resistor value adjustments.

if someone can look this over it advise if I have this right that would be great.

[raygdunn]

If it's been built wrong, then all bets are off. Was just pointing out that this is not a nice way to treat logic ICs. It's an old schematic and it was most likely a noticeable saving in parts and assembly to omit voltage underswing protection. Low current outputs are a blessing in this sense.

Where was the scope common connected in the above picture, raydgunn?

The unadjusted trace, To fit now 2V per grid unit rather than 1V.
(Noisy as wife watching TV :-) )
Sample pulse seems to have the expected voltage, which I'd guess was the reason for asking.

Ray

[Old cart]

The unadjusted trace, To fit now 2V per grid unit rather than 1V.
[ATTACH]35552[/ATTACH] (Noisy as wife watching TV :-) )
Sample pulse seems to have the expected voltage, which I'd guess was the reason for asking.

Ray

Ray, that is a good looking trace, save the TV noise! It does appear as though one of our members has identified the reason why the 40106's get degraded. It is not taking the input put voltage to 0, it is taking the input voltage higher than .5. This can happen on pins 1,3,5. If it gets over .5 it can break some chips. In impulse's case it is over .5V.

A working circuit is a thing of beauty so you may not want to try it but post 325 has a potential solution to the chip breaking problem.
Just to satisfy my curiousity could you measure the DC voltages at pin 1,3, and 5 relative to ground ( pin14)

If if you are not comfortanble doing this that is fine.

[raygdunn]

Ray, that is a good looking trace, save the TV noise! It does appear as though one of our members has identified the reason why the 40106's get degraded. It is not taking the input put voltage to 0, it is taking the input voltage higher than .5. This can happen on pins 1,3,5. If it gets over .5 it can break some chips. In impulse's case it is over .5V.

A working circuit is a thing of beauty so you may not want to try it but post 325 has a potential solution to the chip breaking problem.
Just to satisfy my curiousity could you measure the DC voltages at pin 1,3, and 5 relative to ground ( pin14)

If if you are not comfortanble doing this that is fine.

OK. I have pin 1 at +0.49. So just hanging in there :-)

Readings are:
Pin 1: +0.49
Pin 3: +0.48
Pin 5: -0.12

I'll try the "nip and tuck" operation (post #325) in the morning, when I'm more awake :-).
Looks simple enough and sounds a very good idea. I should mention that my 79L05 only puts out 4.93V. I don't think it is relevant to the readings, or is it?. (It was originally 4.95V and as it was under 5V I assumed it was faulty. I see a post in another thread that says the similar 78L05 can be below 5V, so assume this is not a real problem.)

Ray

[Qiaozhi]

Looks simple enough and sounds a very good idea. I should mention that my 79L05 only puts out 4.93V. I don't think it is relevant to the readings, or is it?. (It was originally 4.95V and as it was under 5V I assumed it was faulty. I see a post in another thread that says the similar 78L05 can be below 5V, so assume this is not a real problem.)

Ray

It's not a problem. The 78L05 has an output voltage tolerance of +/- 5%.

[Old cart]

OK. I have pin 1 at +0.49. So just hanging in there :-)

Readings are:
Pin 1: +0.49
Pin 3: +0.48
Pin 5: -0.12

I'll try the "nip and tuck" operation (post #325) in the morning, when I'm more awake :-).
Looks simple enough and sounds a very good idea. I should mention that my 79L05 only puts out 4.93V. I don't think it is relevant to the readings, or is it?. (It was originally 4.95V and as it was under 5V I assumed it was faulty. I see a post in another thread that says the similar 78L05 can be below 5V, so assume this is not a real problem.)

Ray

Those voltages indicate that the clamp diodes in your device are doing their job. Maybe that is why this chip is working great. Pin 5 is smaller because there is larger resistor in that path. That is normal behavior.