# [sdiy] Triangle wave DCOs?

Tom Wiltshire tom at electricdruid.net
Mon Jan 19 01:30:58 CET 2009

```To solve this problem, you can do what Fredrik Carlqvist did for the
Minod DCO (Saw DCO, SDIY archives, 6 Oct 2004). Use a comparator to
tell the uP when the triangle (ramp in his case) is approaching the
rails. You can then use the uP to find the maximum current you can
supply that still allows the reset pulse to occur before the
comparator trips. Like this you can calibrate the current very
accurately even with a pretty dodgy current source. Fredrik used a
CA3080, which is hardly the most high fidelity device on the planet -
like you said, the advantage of a DCO is the accuracy of frequency
even with a cheap current source.

T.

On 18 Jan 2009, at 18:02, harrybissell at wowway.com wrote:

> If the ramp current source was too large, you would reach the
> positive rail
> before the reset pulse came. resulting in a flat topped pulse. Too
> small and
> the amplitude would be lower.  Both of these are not obvious to the
> ear.
>
> The triangle wave, if the current was off, could eventually drift
> toward
> either rail. At some point you change frequency and that could
> leave you with
> a little positive or negative offset. If you hit a rail, it will
> flat top a
> triangle and drastically change the sound, you will hear that...
>
> If your current source was really 'that' good... you could make it
> a VCO
> instead of a DCO. The advantage of the DCO is the accuracy of
> frequency is
> guaranteed with a cheap current source and an accurate reset
> frequency reference.
>
> H^) harry
>
>
>
>
>
> On Sat, 17 Jan 2009 20:28:11 +0000, Tom Wiltshire wrote
>> I don't understand how you're going to get any asymmetry if it's
>> being switched by a microprocessor. The one thing you can be damn
>> sure of is that the time going up and the time going down are the
>> same. Assuming you don't change the current, that'll guarantee the
>> symmetry, won't it? The amplitude compensation is still a problem,
>> but that's the same for ramp DCOs, and isn't that hard to solve.
>>
>> Still, like Aaron, I can't see any particular advantage over a ramp-
>> reset DCO.
>>
>> T.
>>
>> On 17 Jan 2009, at 18:09, harrybissell at wowway.com wrote:
>>
>>> sounds tricky. errors in the ramp would be in amplitude in one
>>> direction... the triangle could clip at either rail... Asymmetry in
>>> a triangle would be MUCH more obvious than a sawtooth
>>>
>>> H^) harry
>>>
>>>
>>>
>>> On Fri, 16 Jan 2009 23:07:35 -0500, Aaron Lanterman wrote
>>>> I was reading through some of the traffic on DCOs (typified by
>>>> ramp-
>>>> with-microprocessor-controlled-reset type sawtooth cores), and was
>>>> wondering... anyone know of any similar designs for triangle cores,
>>>> where say a microprocessor is responsible for deciding when to
>>>> switch  the direction of the current going into the integrator?
>>>> Basically,  something like a Buchla VCO, but with a microprocessor
>>>> decided when to  trip the switch instead of a comparator.
>>>>
>>>> I can't think of any particular advantage of such a scheme over a
>>>> ramp- with-reset, but there might be something I'm overlooking.
>>>>
>>>> - Aaron
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>>>
>>>
>>> Harry Bissell & Nora Abdullah 4eva
>>>
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>
>
> Harry Bissell & Nora Abdullah 4eva
>
>

```