DAC object

WaldoDTD

So I was wondering how best to make a DAC that is able to control an outside power source I need voltages above 5V and can't use the DAC voltage class is there a chip that will be able to discern pulsetrains that are written to the pin? Also is it possible to have the pin pulse a transistor's base pin while the collector and emitter are connected to a different power source/common. Also is there any way to add IO ports to the Javelin stamp? I seem to recall an appmod for this at one point but can't find it. Thanks!-Waldo

Post Edited (WaldoDTD) : 10/9/2008 1:40:03 AM GMT

Peter Verkaik

You can still use the DAC class. Just amplify the output voltage 0-5V with
a noninverting opamp (or transistor) circuitry. Resolution of course remains limited to 8bits.
For additional outputs you can use shiftregisters like HC595. For these
there are classes as well.

regards peter

WaldoDTD

so I have been looking over everything, the load requires a very high current (4A) so i don't think the opamp would be a viable option, instead i am thinking of maybe a optocoupler and sending a PWM signal to the diode end to influence another higher powered circuit.

Peter Verkaik

The idea is to use an opamp to amplify the voltage and then
use the opamp output to control the base of a power transistor which
will deliver the current.

························· +12V
PWM output o

---

+······ / c
(0-5V)············· >--b-| NPN transistor
··········+

---

·-······ \ e
··········|·············· +---[noparse][[/noparse]load]

---

+
··········|···············|·············· |
··········|···············+--[noparse][[/noparse]R2]-+-[noparse][[/noparse]R1]--+
··········|······················ |······ V GND
··········+

---

+

regards peter

Post Edited (Peter Verkaik) : 10/9/2008 7:40:30 PM GMT

WaldoDTD

thank you, sorry for the lapse,

Would it be possible to build a circuit where the stamp only has to write a hexadecimal number to a pin and have that number correlate to gates on an IC is this a shift register?
could you explain the above circuit a little more i assume that this is a simple opamp circuit with the gains R2/R1.

I am assuming that the shift register mentioned above would be what i am looking for where i "write a number" to an IC, I assume that I set the Javelin and the register to an external clock so that everything is synced as well.

Post Edited (WaldoDTD) : 8/16/2009 11:11:34 AM GMT

Peter Verkaik

The opamp circuit is a non-inverting opamp with gain (R2+R1)/R1
If you just need to switch power you could use

·················+12V
···················|
················[noparse][[/noparse]load]
···················|
···················/c
JavPin o---[noparse][[/noparse]1k]--b|
·················· \e
·················· |
·················· V GND

A shiftregister requires a clockpin and a datapin. The number you write (using shiftOut)
are the levels of the output pins of the shiftregister. You can cascade shiftregisters
to add more output pins. To prevent ripple across output pins you also need a
javelinpin to control the latch of the shiftregister. See datasheet of 74HC595.

regards peter

kwinn

Sound like you want an actual DAC chip with SPI interface. Take a look at http://www.national.com/analog/adc/low_power_dac

Prettybird

An LM 311 is a comparitor that can easily boost the pulsetrain up to 15V from a simple TTL signal. It can also easily drive 100MA. From there, you would have to add transistors. They are hi freq. too. Is a pulsing DC good enough? We have used them in the oscilator section for EDM machinery that would burn metal under oil with 90 VDC up to about 80 amps, using a designed shaped carbon electrode. Typical was around 10 to 20 amps for a finer finish. It was all in the duity cycle. You might want an ajustable one shot from the LM311 to the transistors to help you with that.

Post Edited (Prettybird) : 8/19/2009 2:21:48 PM GMT