TP1 voltage too low

[Qiaozhi]

Sorry i'm pretty new to electronics which pins are analog gates of the IC7a/b? Also i have noticed that by adjusting R18 i can only go to -1.1v and up to +1.9v, according to the guide it should be +1.6v to -1.6v....

IC7 contains four analog gates. IC7a and IC7b are two of these gates. Pins 5 and 13 are the gate control pins, and these are switched by Q8 and Q9. If you remove Q8 and Q9, the analog gate control pins will be pulled high by the two 10k pull-up resistors (R44 and R48 ), which turns these gates on.

The actual range of values obtained with the null-offset pot (R18 ) are not that important, as long as the offset can be adjusted to 0V. In your case this appears to be OK.

[macross]

IC7 contains four analog gates. IC7a and IC7b are two of these gates. Pins 5 and 13 are the gate control pins, and these are switched by Q8 and Q9. If you remove Q8 and Q9, the analog gate control pins will be pulled high by the two 10k pull-up resistors (R44 and R48 ), which turns these gates on.

The actual range of values obtained with the null-offset pot (R18 ) are not that important, as long as the offset can be adjusted to 0V. In your case this appears to be OK.

IC7 pins 5 and 13 are +5v.

[Qiaozhi]

IC7 pins 5 and 13 are +5v.

If there is +5V on the pins 5 and 13, then the analog gates should be turned on.
What voltage do you have at TP4, and also at IC7 pins 2 and 3?

[macross]

If there is +5V on the pins 5 and 13, then the analog gates should be turned on.
What voltage do you have at TP4, and also at IC7 pins 2 and 3?

TP4 - 1.9V
IC7 - PIN2 - 1.9v, PIN3 - 1.9v

[macross]

Bump still having same issue. I also noticed that i can adjust both TP4 and IC8 pins 2&3 to 0v with R18 alone.... And R23 just doesn't do anything.

[Qiaozhi]

TP4 - 1.9V
IC7 - PIN2 - 1.9v, PIN3 - 1.9v

In that case it appears that the analog gates are turned on, which is good.
Please can you confirm that you have IC8 removed, and have pin 1 and pin 4 shorted together.
Once you've done this, measure the voltage between pins 2 and 3 with a voltmeter. This voltage will change when you adjust R23, and needs to be set to zero.

If this doesn't work, then I've no idea what's wrong.
With the setup described above, the circuit is reduced to two resistor dividers in parallel. R23 is acting as the top resistor in each divider network, so adjusting this pot will change the voltage in each leg. To allow for the effect of resistor tolerances, R23 needs to be set to balance the two networks such that the difference in voltage is zero.

[Carl-NC]

I don't see the problem. Qiaozhi has a good reminder that when you adjust R23 you want to measure the voltage between IC8.2 and IC8.3, not their individual voltage levels. The individual levels won't change much, but the difference will.

[macross]

So i have fully assembled the board as per instruction, but now it's doesn't react to metal objects. In troubleshooting section of the guide it says that TP9 should be 0v for no target, but i'm getting 4.2v all the time. If i move large metalic object over the coil then voltage shifts to negative -3.5v. Also threshold worked for some time but now it doesn't. Speakers just scream all the time.

[Qiaozhi]

So i have fully assembled the board as per instruction, but now it's doesn't react to metal objects. In troubleshooting section of the guide it says that TP9 should be 0v for no target, but i'm getting 4.2v all the time. If i move large metalic object over the coil then voltage shifts to negative -3.5v. Also threshold worked for some time but now it doesn't. Speakers just scream all the time.

Do you have an oscilloscope?

[macross]

Do you have an oscilloscope?

Yes i do have an oscilloscope.

[Qiaozhi]

Yes i do have an oscilloscope.

Many people attempt to build a complex project like Hammerhead with only a DVM for debugging, and wonder why they have so much trouble. Often they end up disillusioned and then give up. So it's good that you have an oscilloscope. At least we have a chance of getting your detector working.

First things first: Are all the power supplies at the correct voltage? i.e. What voltages are on IC2 pin 1 (across C5), IC3 pin 3 (across C6) and IC4 pin 3 (across C7)?
Note that the battery +ve is actually the ground reference in this design. You might be surprised how many people are confused by this.

Can you then post the waveforms at TP1 and TP2?

[macross]

Many people attempt to build a complex project like Hammerhead with only a DVM for debugging, and wonder why they have so much trouble. Often they end up disillusioned and then give up. So it's good that you have an oscilloscope. At least we have a chance of getting your detector working.

First things first: Are all the power supplies at the correct voltage? i.e. What voltages are on IC2 pin 1 (across C5), IC3 pin 3 (across C6) and IC4 pin 3 (across C7)?
Note that the battery +ve is actually the ground reference in this design. You might be surprised how many people are confused by this.

Can you then post the waveforms at TP1 and TP2?

Well to be honest i almost abandoned this project also, when Carl asked if i have an oscilloscope. It was a pain for my wallet, but a scope is worth every penny when your hobby is about electronics.

Voltages:
IC2 pin1 - (+5v)
IC3 pin3 - (-5v)
IC4 pin3 - (-5v)

Waveforms:

TP1:https://imageshack.us/scaled/large/689/tp1kt.jpg

TP2:
As for this one should the coil be connected when taking a waveform? And what about fly back voltages? Can those damage the scope? (Better to ask more question than to be sorry when something goes wrong)

Also i am a bit confused about jumpers which to short. In the guide it says "plus any needed jumpers", but i'm confused which to short. Right now i have two jumpers shorted... First one is near Q1, Q2 and second one is near TP2, but there are two more jumpers on the board near R53 and Q7.

And last question how many Ohms should the speaker be for the audio output? I tried connecting a pair of cheap headphones and it just fried those.

Thanks for being patient with newbies i really appreciate it.

[Carl-NC]

If you haven't resolved the R23 problem, then building out the rest of the circuit gave expected results. You need to back up and figure that out.

[Carl-NC]

TP1 looks fine. TP2 can be viewed on the oscope with a coil attached; most scopes have a ~400V max rating, and if you use a 10X probe the flyback will be well below this.

"Needed jumpers" depends on what options you are building. I think the default build per the instructions specifies the needed jumpers. On the speaker, just about any speaker will work, unless the circuit isn't working right, in which case just about any speaker can burn up. If you want to play it safe, put a large cap (100uF) in series with the speaker.

- Carl

[Qiaozhi]

As Carl said, the waveform at TP1 looks OK.

As far as the jumpers are concerned, let's get the transmitter working first:
1. If you've fitted R8, then remove it and replace with a short circuit.
2. Add a jumper to connect the gate of Q3 to the junction of R8 and R9.

The transmit circuit should now match the one shown in Figure 5.

Construct a mono coil, as described on page 9, and fit a 680R 1W resistor in place of R11.
Set your scope probe to 10x and connect to TP2. Then post the waveform here.

By the way, it is better if you attach the images directly in the forum using the Manage Attachments button (Go Advanced), as any images hosted off-site will tend to disappear over time.