hello

FreeEMS topics that aren't specific to hardware development or firmware development.
User avatar
Fred
Moderator
Posts: 15431
Joined: Tue Jan 15, 2008 2:31 pm
Location: Home sweet home!
Contact:

Re: hello

Post by Fred »

NinjaRider wrote:thus the reason to my question about using multiple dac's which thanks to google i kinda answered myself. i would just need 12 pins to act as the serial com to the dac's. depending on the solenoid design i make i might need an amp after the dac to boost the amp's the solenoids receive.
For the last time, PWM:

Pulse
Width
Modulation

Pee
Double You
Em

Now I'm just going to sit back and watch you do whatever you want to do, could be good entertainment :-)

Fred.
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!
NinjaRider
DIP8 - Involved
Posts: 24
Joined: Wed Feb 22, 2012 4:51 am

Re: hello

Post by NinjaRider »

pwm states would either be open or closed, unless im mistaken. i need multiple states inbetween.
User avatar
Fred
Moderator
Posts: 15431
Joined: Tue Jan 15, 2008 2:31 pm
Location: Home sweet home!
Contact:

Re: hello

Post by Fred »

You're mistaken.
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!
Peter
LQFP144 - On Top Of The Game
Posts: 268
Joined: Tue Dec 27, 2011 5:37 am

Re: hello

Post by Peter »

From https://en.wikipedia.org/wiki/Digital-t ... _converter
Under DAC types
"The pulse-width modulator, the simplest DAC type. A stable current or voltage is switched into a low-pass analog filter with a duration determined by the digital input code. This technique is often used for electric motor speed control, but has many other applications as well."
:-p
MotoFab
1N4001 - Signed up
Posts: 307
Joined: Thu May 29, 2008 1:23 am
Location: Long Beach CA

Re: hello

Post by MotoFab »

NinjaRider wrote:which if it were up to me and i had the time to spending doing it. i would dispose of said iac and use a vaccum bypass much how the 2003 zx-6rr is setup.
All valve-based idle air control systems are 'bypass' devices. The idle air bypasses the throttle butterfly, or throttle slide.

There are other ways to change or control idle speed that operate the throttle butterfly directly, such as using the throttle-by-wire servo to control idle speed. But that's prolly outside the scope for now.
MotoFab
1N4001 - Signed up
Posts: 307
Joined: Thu May 29, 2008 1:23 am
Location: Long Beach CA

Re: hello

Post by MotoFab »

Peter wrote:From https://en.wikipedia.org/wiki/Digital-t ... _converter
Under DAC types
"The pulse-width modulator, the simplest DAC type. A stable current or voltage is switched into a low-pass analog filter with a duration determined by the digital input code. This technique is often used for electric motor speed control, but has many other applications as well."
The primary difference/benefit of using PWM to control the solenoid, verses an actual DAC I mean, is that PWM operates the transistor in saturation mode verses ohmic mode.
User avatar
Fred
Moderator
Posts: 15431
Joined: Tue Jan 15, 2008 2:31 pm
Location: Home sweet home!
Contact:

Re: hello

Post by Fred »

MotoFab wrote:The primary difference/benefit of using PWM to control the solenoid, verses an actual DAC I mean, is that you can actually find reasonably priced PWM devices capable of the currents required.
Fixed :-)
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!
MotoFab
1N4001 - Signed up
Posts: 307
Joined: Thu May 29, 2008 1:23 am
Location: Long Beach CA

Re: hello

Post by MotoFab »

The current to operate the solenoid isn't any higher, PWM vs DAC. Operating the transistor in the ohmic (aka linear) range when using DAC control, that's the issue.

For ohmic range operation a larger and more expensive driver is needed to provide enough silicon junction surface area to dissipate the heat generated from the voltage drop across the partially-activated junction.
User avatar
Fred
Moderator
Posts: 15431
Joined: Tue Jan 15, 2008 2:31 pm
Location: Home sweet home!
Contact:

Re: hello

Post by Fred »

All true, and none related to the previous post. The first DAC I clicked on could drive 20mA which is fairly typical. PWM on the other hand is trivial to push out to 100A+. His valves will require an amp or two to operate. DACs to do that are not cheap or even available.
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!
MotoFab
1N4001 - Signed up
Posts: 307
Joined: Thu May 29, 2008 1:23 am
Location: Long Beach CA

Re: hello

Post by MotoFab »

Fred wrote:The first DAC I clicked on could drive 20mA which is fairly typical.
Output pins from processors also typically only drive 20mA, and must be connected to a driver transistor to make a PWM signal that can drive something practical.

In the same way, usual practice puts a current buffer transistor after the high impedance DAC output pin to serve as the DAC driver. Which is identical to the usual practice putting a current buffer transistor after the processor output pin to serve as a the PWM driver.

It isn't about the greater current requirements, as you mentioned. Because the current through the idle air solenoid output transistor, whether DAC or PWM, is the same in both cases. It's operating the driver in the ohmic range that requires the more expensive transistor.
Post Reply