HH2 -- first cut

[Carl-NC]

For the most part, HH2 is the same as HH1 except that the main 555 oscillator and 74221 chips have all been replaced with a PIC 12F683. Why did I chose this part? Because it is small (8 pins), and offers the option of trying out the ADC and PWM for audio generation.

Also, I did a few minor updates, namely adding a class B driver for the MOSFET, a drain diode on the MOSFET, and a feedback clamp diode. These should help those who are trying to wring out minimal sample delays.

- Carl

[Carl-NC]

Here is a 150dpi GIF (PDF above is 300dpi):

[Carl-NC]

Here is the current layout:

[Carl-NC]

Please look over the schematic & layout and post feedback & suggestions. Keep in mind that this is not intended to be a cutting-edge design, but rather a circuit that introduces the use of a PIC for timing control. It is really meant for those who now understand PI basics, but have never used micros.

- Carl

[Carl-NC]

One final note: Unlike HH1, I don't intend to offer PCBs for this project. It's just too time-consuming. But I will post Gerbers for anyone who wants to get a board made, and folks are welcomed to team up to cut costs, or even sell boards on their own. I recommend pcbcart.com for good quality cheap PCBs.

- Carl

[zenit52]

Hi Carl,
Thanks for your idea,
Please tell us about PIC source program in basic or c++ and PIC micro exactly what do in this HH2 circuit?
did we use the same PIC design for Deltapulse circuit ?
With best regards...

[Carl-NC]

To my recollection, the Deltapulse does not use a PIC. In this design, the PIC controls the coil pulse & the sample timing. It is also possible to digitize the analog output and create a VCO audio using the PWM.

The source code will be in C, using the free Microchip C compiler. I did most of the work on this project last year, including the microcode, but never got it finished. When I switched jobs a few months ago I managed to lose the source code, I think it was on my Maxim laptop that I turned in. So I am starting over on that, but it shouldn't take long.

- Carl

[1843]

Hi Carl

Why not to use a 1N4007 instead of 1N4004? The junction capacitance is about half...

[Carl-NC]

Actually, I threw it in as a placeholder... I haven't researched low-cap diodes. The 4007 is probably fine.

- Carl

[ivconic]

I like what i see on this schematic, also i like the way pcb is projected.
So... only code we need to start making this. Looking forward.
Regards!

[barry]

keeping a keen eye on this one. looking forward to the source code.

[Aziz]

MOSFET fast switch-off circuit proposal with FET's

Hi Carl,

I recently analysed the totem pole MOSFET driver of the HH. This can be optimized using small signal FET's (BS170/BS250). The proposed schematics below is optimized for fast switch-off. It improves the turn-off fall time and turn-off delay time compared to the BJT solution in HH.

The gate charge in the MOSFET IRF740 will be discharged through Q1 (2N2907). R40/R41 resistors can even be omitted.

The performance is almost equal to the standard fast switching MOSFET driver IC's.

Regards,
Aziz

[Andy_F]

I recently analysed the totem pole MOSFET driver of the HH. This can be optimized using small signal FET's (BS170/BS250)...

U14 And U15 in the offered scheme do not do anything (it can be removed). At the same time, in gate X7 it is necessary to put the resistor 10-20 Ohm (protection from latch).

By the way, diode U11 too does not carry out any useful function, only worsens switch (IRF740) characteristics in open state.

[Aziz]

Here is the low cost variant (initiated from Andy) with same switch-off behaviour expect the switch-off delay is extended about 0.5 µs.

The diode and the BJT is important to discharge the MOSFETs gate charge. This cannot be omitted. Switch-on isn't important and can be delayed and be slow for our purpose.

Aziz

[Aziz]

Forgot to mention: Pay attention to the pulse logic level! It is changed with the low cost variant (inverting totem pole gone). So the micro should give right logic levels.

Aziz