In the MS3Base/V3 Hardware Guide -- 3.5.7 Boost control output - diagram on page 48: what is the purpose of the 1N4001 diode to 12v?
How does this differ from the IgbtIn to IgbtOut circuit on page 181 of the same manual (schematics page 5 of 8 )? Once R57 is deleted and R43 is jumped - there is just a direct connection to the CPU pin to drive the transistor. Can the TIP122 be driven the same way? Or does driving a solenoid or shift differ that much from driving a coil?
Last edited by fj1289 on Mon Oct 03, 2016 7:23 am, edited 1 time in total.
It's a flyback diode. Powering up the coil generates a magnetic field - the whole point to the exercise, right? The problem is that when the field collapses, it generates a voltage; if that voltage isn't bled off, it tries to force the solenoid shut. With an injector, this characteristic is used to help cut the fuel flow hard; with a PWM solenoid that you want to stay in some position between 'open' and 'closed', it's a pain. By using the flyback diode to allow this induced voltage to flow back to the top of the solenoid, the pintle tends to stay where you want it.
It's the exact same thing - processor pin to base resistor to base; 'Boost' pin to collector, emitter to ground. The schematic on p. 48 shows the bottom of R43 because that's a nice heavy trace to the ground pins on the DB37.
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QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module TTR Ignition Systems
dontz125 wrote:It's a flyback diode. Powering up the coil generates a magnetic field - the whole point to the exercise, right? The problem is that when the field collapses, it generates a voltage; if that voltage isn't bled off, it tries to force the solenoid shut. With an injector, this characteristic is used to help cut the fuel flow hard; with a PWM solenoid that you want to stay in some position between 'open' and 'closed', it's a pain. By using the flyback diode to allow this induced voltage to flow back to the top of the solenoid, the pintle tends to stay where you want it.
It's the exact same thing - processor pin to base resistor to base; 'Boost' pin to collector, emitter to ground. The schematic on p. 48 shows the bottom of R43 because that's a nice heavy trace to the ground pins on the DB37.
Aha! Now I remember the reason for yet another relay in the system - I reversed the switched lead on the shift solenoid from the negative lead to the positive lead in an effort to eliminate some interference I was getting (synch loss during the shift if I remember correctly). I was told switching the positive side vice the negative side would create less EMI - something about it being absorbed by the engine block? Seemed to help - but it could have been putting the relay (to reverse the uS ground output) between the solenoid and the uS may have been what really helped?
Since the shift solenoid is on/off vice PWM, would I be better off with a diode between the two leads vice (or in addition to) the diode in the circuit?
There really isn't much difference in effect between a diode at the solenoid, and one in the MS. What CAN happen, especially with PWM and if placed poorly inside the case, is that noise from the flyback can cause issues; placing the FB diode at the solenoid can help. As you say, this isn't a PWM device, so noise should be minimal.
Just like picking up a lady in a bar - "What ever works, baby; whatever works!"
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QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module TTR Ignition Systems
Along the lines of whatever works...
Plan to drive a solid state relay for the progressive nitrous output. Can I use a TIP120 vice the 2N2222 shown on page 175 of the MS3Base/V3 Harware Guide? Also, why the 2K resistor vice 1K shown in other circuits?
Different transistors want different amounts of base current for different functions. For something like driving a relay or solenoid, it's more user preference - so long as the transistor comes fully ON, it's all good.
As for the TIP120 vs 2N2222, you could, but there's no particular benefit. When you're driving a relay (SS or otherwise), there's rarely enough current involved to need a higher-power transistor. Unless you're driving some BIG relays ...
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QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module TTR Ignition Systems
The only reason to use something different is the molex adaptor card is setup to easily add four high current ignition circuits (places on the card for inline resistors and VB921/BIP373 on four of the outputs). Since I'm only using two ignition outputs (and using logic level for those!) - I'd like to use that "free real estate" if possible and save the areas on the proto board or head sink for other circuits as needed. If the 2N2222 will respond better or is better suited for this use, I can "twist" the leads to suit the TO-220 foot print on the card.
Picked up a couple proto boards from Radio Shack last night to experiment with and use for all the input circuits. I'm sure someone with more experience than me could figure out clever ways to get it all on the V3.0 board -- I'm taking the easy way out!
Last night removed the output circuits I had built - figured out better ways of doing it and was not happy with some of the component placement and a few of my solder joints as a result.
Still working on figuring out the "art of the possible" here...
