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Lego Throttle Blaster

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First post, by wbahnassi

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Me and my brother wanted to try out a Throttle Blaster for some of our builds. I decided to build one without using the github PCB, as I don't need all the options that are offered by it. I just went directly to the rotary encoder and thus ignored all jumpers.. and instead I hard-coded their values in the firmware.

The result was just a Pico and the LED display with 4 dupont wires between the two. The Pico also extends one wire carrying 3 lines out to the PC. These are +5V, gnd and the line that goes to the CPU HLT.

My brother has an IBM PC 300GL NLX desktop with a P2 400Mhz CPU. Unless you mod the case, there is no convenient place to install the Throttle Blaster, so we went the fully external way.

Similar to my adventures with Lego (Lego PC - Traditional Damascus Theme) he went ahead and designed a prototype Lego case to house the TB.. this time the design is inspired by a well-known Midi device.

The device works great! Huge thanks to Scrap Computing for his great work and sharing this project.

Some Lego pieces are still temporary placeholders, like the transparent blocks, until we get the pieces in black. But overall it came out nice and sturdy.

Turbo XT 12MHz, 8-bit VGA, Dual 360K drives
Intel 386 DX-33, Speedstar 24X, SB 1.5, 1x CD
Intel 486 DX2-66, CL5428 VLB, SBPro 2, 2x CD
Intel Pentium 90, Matrox Millenium 2, SB16, 4x CD
HP Z400, Xeon 3.46GHz, YMF-744, Voodoo3, RTX2080Ti

Reply 1 of 7, by jh80

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Very nice! Looks great.

Reply 2 of 7, by RetroPCCupboard

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Nice. I have considered adding one of these to my Pentium MMX system to allow it to run XT-class games. Have you tried it for this purpose?

Reply 3 of 7, by wbahnassi

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Yes. It goes down all the way to 4.77Mhz. I tried it on a few speed sensitive games. Here are the ThrottleBlaster speeds I found to be best:
* Duck Tales - best on 10MHz
* Bad Dudes - best on 8MHz
* Test Drive 3 - best on 25MHz

I still haven't gotten to tougher tests. Digger, Might & Magic 1..
For the games above setting the TB to 4MHz felt than slower than original XT.
The math used to generate the halt signal is actually quite good, but not perfect. The device gives fine control also in addition to the presets. Overall, I highly recommend it.
I plan to make one for my 233MMX as well as my P3 1GHz. The convenience of switching speed on the fly is amazing.

Turbo XT 12MHz, 8-bit VGA, Dual 360K drives
Intel 386 DX-33, Speedstar 24X, SB 1.5, 1x CD
Intel 486 DX2-66, CL5428 VLB, SBPro 2, 2x CD
Intel Pentium 90, Matrox Millenium 2, SB16, 4x CD
HP Z400, Xeon 3.46GHz, YMF-744, Voodoo3, RTX2080Ti

Reply 4 of 7, by RetroPCCupboard

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wbahnassi wrote on 2026-03-28, 16:23:
Yes. It goes down all the way to 4.77Mhz. I tried it on a few speed sensitive games. Here are the ThrottleBlaster speeds I found […]
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Yes. It goes down all the way to 4.77Mhz. I tried it on a few speed sensitive games. Here are the ThrottleBlaster speeds I found to be best:
* Duck Tales - best on 10MHz
* Bad Dudes - best on 8MHz
* Test Drive 3 - best on 25MHz

I still haven't gotten to tougher tests. Digger, Might & Magic 1..
For the games above setting the TB to 4MHz felt than slower than original XT.
The math used to generate the halt signal is actually quite good, but not perfect. The device gives fine control also in addition to the presets. Overall, I highly recommend it.
I plan to make one for my 233MMX as well as my P3 1GHz. The convenience of switching speed on the fly is amazing.

Interesting that it seems slower than the XT given that newer processors should do more instructions per clock and they have wider bus width.

A few games that I have had problems on my MMX are:

Burger Time (i think it crashes)
Sopwith
Metropolis (by Melbourne House)
Bouncing Babies

Reply 5 of 7, by NeoG_

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RetroPCCupboard wrote on 2026-03-28, 19:12:

Interesting that it seems slower than the XT given that newer processors should do more instructions per clock and they have wider bus width.

I would guess that the calculation for the signal timing gets less accurate when using really small values relative to the original CPU speed

98/DOS Rig: BabyAT AladdinV, K6-2+/550, V3 2000, 128MB PC100, 20GB HDD, 128GB SD2IDE, SB Live!, SB16-SCSI, PicoGUS, WP32 McCake, iNFRA CD, ZIP100
XP Rig: Lian Li PC-10 ATX, Gigabyte X38-DQ6, Core2Duo E6850, ATi HD5870, 2GB DDR2, 2TB HDD, X-Fi XtremeGamer

Reply 6 of 7, by wbahnassi

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Yes. I find it great that it is able to get very close results while being so flexible. At first I set the "real" speed (400MHz in this case), and the TB calculates the proper timings down from there.
In case the presets aren't perfect, it is possible to switch to fine-tuning mode and change the timings 1MHz at a time.

Turbo XT 12MHz, 8-bit VGA, Dual 360K drives
Intel 386 DX-33, Speedstar 24X, SB 1.5, 1x CD
Intel 486 DX2-66, CL5428 VLB, SBPro 2, 2x CD
Intel Pentium 90, Matrox Millenium 2, SB16, 4x CD
HP Z400, Xeon 3.46GHz, YMF-744, Voodoo3, RTX2080Ti

Reply 7 of 7, by rasz_pl

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RetroPCCupboard wrote on 2026-03-28, 19:12:

Interesting that it seems slower than the XT given that newer processors should do more instructions per clock and they have wider bus width.

newer processors aggressively pre-fill and flush Caches. At that low clock speed most of the time might be taken by that 😀

https://github.com/raszpl/sigrok-disk FM/MFM/RLL decoder
https://github.com/raszpl/FIC-486-GAC-2-Cache-Module (AT&T Globalyst)
https://github.com/raszpl/386RC-16 ram board
https://github.com/raszpl/440BX Reference Design adapted to Kicad