Everyone seems to have this same question. The answer linked is correct as far as I know. You are not forced to qualify/certify your Bluetooth device under the Bluetooth SIG, but if you don't then you're not licensed to use the Bluetooth trademark.
"The Bluetooth SIG does not force members to use the trademark on products incorporating Bluetooth technology, but if the trademark is used then it can ONLY be used by a member of the Bluetooth SIG and for a properly declared product."
Source: https://www.bluetooth.org/en-us/Pages/compliance-program.aspx
There seems to be conflicting information scattered about on the web but we couldn't find anywhere where Bluetooth SIG says you have to qualify the product.
"If I don't put the Bluetooth logo on my product, do I still need to list my product with Bluetooth SIG?
Yes. In all products that incorporate Bluetooth IP must adhere to the Bluetooth Compliance Program. Details on this program can be found on the Bluetooth SIG site."
Source: http://processors.wiki.ti.com/index.php/How_to_Certify_your_Bluetooth_product
I'm not sure how accurate TI's answer here is. More than likely they just want Bluetooth SIG to get the money. The chip, subsystem, PHY, stack, etc. has already been qualified/certified.
Compliance Enforcement -- I did ask "what if I don't use a trademark, nor mention Bluetooth is being used" Never got a response.
Source: http://www.microchip.com/forums/m891671.aspx
I personally know someone with a product on the market where he simply does not market it as being a Bluetooth device.
What if the logo isn't used in marketing materials except for textual mentions, e.g., "Technical requirements: Bluetooth 4.0 enabled phone"?
The compliance enforcement does mention using the word "Bluetooth" as being a part of the trademark. "The Bluetooth® trademarks—logos and the word "Bluetooth"—are owned by the Bluetooth SIG." Source: https://www.bluetooth.org/en-us/test-qualification/qualification-overview/qualification-enforcement-program
However, I don't think the acronym BLE is trademarked, they dropped Bluetooth Low Energy in favor of "Bluetooth Smart", so you could probably get away with using "BLE", which everyone associates with Bluetooth 4.0.
I see 2 possible problems, one of them already pointed out by The Photon. They both have a common theme and that is the base of 'Q' is being overdriven by either the voltage being turned up too high, so the BE voltage of Q is locked at about .7 volts, or the simulated tach signal is overdriving the base, causing the same saturation effect.
Try increasing the 10K base resistor to 22K and add a resistor of 2.2K in series with the simulated signal. This way you should get a square wave at the base of Q that is counted properly, and the base of Q is less likely to be saturated ON by either the 12 volt feed or the simulated tach signal. I can see that your using a base pull-up resistor so if the simulated tach input is disconnected the base of Q will not float and be unpredictable or affect the normal tach input.
Your 'yellow' resistor should be 1K if possible, as it is driving a voltage divider through a diode, with the output clamped at 5 volts. Maximum current through Q is 12mA at 12 volts or about .144 watts, but some of this is sent to the voltage divider.
Best Answer
The circuit, even with the diode is a piece of junk. The 11ms time constant without the diode was pretty short.
Either regulate the supply so it doesn't drop during cranking or use a proper reset chip that provides a timed reset pulse of appropriate duration for a complete reset for any brownout of the supply.