HammerHead Rev D

[Carl-NC]

Since enough folks have asked for PCBs, I decided to make another batch. However, I wanted to add a few enhancements to the design. They are:

• Option for mono coil or seperate TX/RX coils
• Added a diode to the master clock 555 to make it easier to flip the duty cycle. (Useful for active pulldown)
• Added a low battery indicator.
• Changed the audio for non-VCO option. The 555 that is normally used for VCO is now used for non-VCO to set the audio duty cycle when the audio frequency is synced to the clock. You can also use the 555 to run the audio at an entirely different frequency than the audio, useful when you want to use a clock outside the preferred audio range.

I ended up doing a complete relayout, and decided to use 2-sided routing to make life easier (no jumpers). I've only today finished this, and am still looking things over for errors. Also, the new enhancements are entirely untested, so I need to build them up to ensure proper operation.

Attached are the schematic and PCB. Feedback encouraged.

- Carl

[Ray-NM]

Carl
I had a problem which could be just the components that I used. I had to switch R30 to 39k and R32 to 39k to get the threshold to work properly. What happened is I could not reduce the output of Ic8b pin 7 to produce zero ouput from the audio. Also thought about 2 test point pads 1 for N5 and 1 for N6. I like the low voltage indicator, and the options for mono or dual coils. Also the options for the audio.
One thing I do not see are pads in the schematic for a damping resistor on the dual coil option.
Was wondering also about an option for R13 with 2 resistors with the addition of a 100k with pads for a switch to change the gain of the preamp. Was not sure if this idea would add to much noise or not. But then along with that you would have to add the same thing for r26 and R27 to swap in resistors to increase the gain of IC8a to compensate. yeah probably would add a little to much complication to it as then you would need matched components.
Just my thoughts on it. But then I will take whatever you come up with.
Thanks for doing the new bds.
RayNM

[bbsailor]

Rev D Feedback

Carl,

You did great work on the new board. I like the independent audio frequency.

1. Ray-NN made a good catch on the need for a damping resistor (Rd) for L2, the RX coil. This resistor could be a smaller size so it would be easier to squeeze in.

2. Since IC 9 can now be used to provide an independent audio frequency, it should be adjustable to optimize the best frequency for a particular set of headphones and/or individual hearing capabilities. This could be done by using R55 as a frequency limit resistor and placing a trimmer or external pot connection in series with it.

3. Several posts have mentioned the interaction of the audio circuit current draw with the stability of other circuit components. This could be offset by providing the option of powering Q7 and Q11 from an external 9V battery. This could be done by cutting the trace between Q11 and +12 making a short jumper to power it from a single voltage source or open to power it from a separate 9V battery. Also, making this point available to an external 9V regulated supply might offset the audio interaction.

Thanks for your efforts.

bbsailor

[1843]

HH RevD

Hi Carl,
It is better that pins 10, 11 & 12 of IC7 shorted to GND.



Thanks for your work!
Very nice job

[Carl-NC]

I had a problem which could be just the components that I used. I had to switch R30 to 39k and R32 to 39k to get the threshold to work properly. What happened is I could not reduce the output of Ic8b pin 7 to produce zero ouput from the audio.

I might have the values too close to account for tolerances.

Also thought about 2 test point pads 1 for N5 and 1 for N6.

I'll try.

One thing I do not see are pads in the schematic for a damping resistor on the dual coil option.

Originally I forgot to add this. Once I realized it, I was way past that point in the layout, and decided that putting the RX damping resistor in the coil is probably better anyway. Reg posted about this recently. Anyway, I might take another look, but if it's not a relatively easy change I'll probably leave it as is.

Was wondering also about an option for R13 with 2 resistors with the addition of a 100k with pads for a switch to change the gain of the preamp. Was not sure if this idea would add to much noise or not. But then along with that you would have to add the same thing for r26 and R27 to swap in resistors to increase the gain of IC8a to compensate. yeah probably would add a little to much complication to it as then you would need matched components.

Definitely can't do this.

2. Since IC 9 can now be used to provide an independent audio frequency, it should be adjustable to optimize the best frequency for a particular set of headphones and/or individual hearing capabilities. This could be done by using R55 as a frequency limit resistor and placing a trimmer or external pot connection in series with it.

I did think about this, and decided to use fixed resistors, mostly because I didn't have room for another pot. Also, the audio frequency is something that few people would care to have adjustable... use a temp. pot to figure out what you want, then replace with fixed resistors.

3. Several posts have mentioned the interaction of the audio circuit current draw with the stability of other circuit components. This could be offset by providing the option of powering Q7 and Q11 from an external 9V battery. This could be done by cutting the trace between Q11 and +12 making a short jumper to power it from a single voltage source or open to power it from a separate 9V battery. Also, making this point available to an external 9V regulated supply might offset the audio interaction.

I haven't seen this problem, though I won't deny it is possible. However, and 2nd audio-only battery is simple to add with no PCB changes. Just connect the -VB side on the speaker to the (-) side of the 9v battery, and connect the (+) side to a 2nd pole on SW1 to ground.

------------------------------------

My goal is to send out for PCBs early next week. I will order at least 50.

- Carl

[Carl-NC]

It is better that pins 10, 11 & 12 of IC7 shorted to GND.

I thought about doing this in an earlier rev, but I left the pins open in case someone wants to hot-wire the unused switch for some reason.

- Carl

[Carl-NC]

OK, I squoze in an RX damping resistor and TPs for N5 & N6.

[Carl-NC]

(100) boards were ordered today. (!!) They have a 10-day turn around. As soon as they are in, I will probably build one to make sure everything is good before I begin selling any.

- Carl

[Charles (Upstate NY)]

(100) boards were ordered today. (!!)

That's great news! I have parts enough for two boards on order, should be here Friday. Guess I'll play with the new LCD and Microchip PIC until then. The 80 pin TQFP chip should test my soldering skills.

[Ray-NM]

Status of new PCB's

Carl any status on the new pcb's?
Are you building one up as I send this?
RayNM

[Carl-NC]

Good News! I got a call from the fab house just today, PCBs are shipping. I should have them Friday. I'll build one up over the weekend and, hopefully, I can give the go-ahead for orders on Monday.

- Carl

[Carl-NC]

Boards arrived Thursday, got one built Thurs. night, started checking it out today. So far, no screw-ups... it's working. I've only tested the VCO audio, and it sounds like a tea kettle, so I must have something slightly off. I'll try to wrap it up tomorrow so I can give the go-ahead for orders.

Thanks for everyone's patience!

- Carl

[Buzz(ID)]

Carl
Checks in the mail

Buzz

[Buzz(ID)]

Audio Taper

Hi Carl
Could you explain about R41 audio taper, it looks like a regular trimpot to me? Thanks for the fast shipment on the HH PCB, very professionally done.
Nice job!!
Thanks

Buzz

[Carl-NC]

I put all pots down as trimpots, so you can use a trimpot if you don't want to use a panel-mount pot. Even though R41 is spec'd as a 5k audio taper, use could use a LT trimpot if you intend to set it to a fixed volume level.

Using trimpots also lets me build bench protos with all components neatly on the board.

- Carl