Telescope Drive Master – Milestones of Evolution

•    TDMv1.x – the very first commercial versions; it was sold (just a couple of dozen pieces, mainly within Hungary) from 2007 before our exclusive contract signed with Meade Europe. This version did not have auto-guider input and both LX200 standard TTL (TDM Out1) and SBIG ST4 relay contact (TDM Out2) outputs provided RA control signals only. Its system-resolution is 1/8” (or 0.125 arc-second); control range limitation in tracking mode is +/-4” and display range of PED (Periodic Error Display) mode is +/-16”. In case of optimal circumstances, the best achievable guiding accuracy is (or a bit less then) +/-0.5”. “TDM Monitor v1.0” software can be used for PE display or tracking error display on PC screen; USART port provides tracking error codes on 1Hz frequency. (Remark: only different features compared to these ones will be explained in case of newer versions below.)

•    TDMv2.2 – this is the first “Meade-related” version. This version has auto-guider input but just TDM Out1 output provides TTL control signals for both RA and declination directions. It means that auto-guider’s declination pulses are not transmitted via TDM Out2 (relay contact).

•    TDMv2.3 – the “mount tester” version with extended measurement range (+/-32” instead of +/-16”) but reduced resolution (1/4” instead of 1/8”). This is better for this purpose because several mount-types of the commercial mount manufacturers have quite high amplitude of periodic error. (Important: “TDM Monitor v2.31” software has to be used for this TDM version to provide correct display scale.) In this way, this version of TDM will be able to display such a high PE without reset.

•    TDMv2.4 – “lazy” version for LX200Classic and for any other mount-controller witch has 1x (but no lower) sidereal guide speed only. (But this version can provide guiding accuracy between +/-1 and +/-2 arc-seconds only.)

•    TDMv2.5 – this is the new (existing) version from 2012.

- This variant has “built-in relay box” so both TDM Out1 (TTL) and TDM Out2 (relay contact) can be used for both RA and declination control (in declination just together with auto-guider support) without any limitations. This is why, additional two LEDs have been installed in the lower right corner of the box to indicate the tracking corrections in declination. The color codes of these tracking correction LEDs fit to the auto-guider cabling standard colors: Red -> -RA; Green -> -Decl; Yellow -> +Decl; Blue -> +RA.

- If active low TTL signal is applied simultaneously on both RA+ and RA- contacts of TDM's Auto-guider Input (Ra+ to Gnd AND Ra- to Gnd), the TDM will be switched to "external prohibited mode" during this control configuration. In this way, similarly to external auto-guiding systems, a pulse guide based guiding software (e.g. EQMOD) can also automatically switch TDM control algorithm off during the corrections of its own and, after this interaction, TDM will immediately run a self-reset and will keep the new position. This function can also be used for image dithering (to create smooth image background with multi exposures), avoiding TDM compensations during these tiny movements.

- Previous versions had roughly one digit (0.125") permanent offset which did not cause any practical problem in tracking but, based on Mr. Jerry Hubbell's extremely precise tests, we corrected this offset to zero in this version.

- The USART output refreshing frequency of this version is higher (10Hz) in 5Hz control frequency mode (Jumper3 "on"). In 1Hz control frequency mode (Jumper3 "off"), output communication frequency remained 1Hz (like in case of previous versions). But please do not be confused! TDM control frequencies (1Hz or 5Hz) have not changed; just the serial port output frequency increased (1Hz or 10Hz, depending on Jumper3 setting) so the tracking error can be followed in much tighter way. If you want to enjoy this improvement, you need to download Jerry's monitor software (instead on TDM Monitor from this site). See below.

- Additionally, extended control range limitation (+/-10” instead of +/-4") can tolerate more aggressive blasts of wind without auto-reset.

Mr. Jerry Hubbell’s “TDM TE recorder” software can be used for visualization:

http://www.explorescientific.com/jerry_hubbell/TDM_TE_Recorder_106b.zip

•    TDMv2.51 – No "improvements" but it contains a few PIC firmware corrections for v2.5 and repairing earlier bugs

- Jumper #1 positions (Sidereal-Avg. King rate) were reversed in the previous versions. From this PIC, it is corrected.

- In a few and very special cases, when the mount tracking curve is thorny, drizzling or shaking too much (when the tracking speed of poor quality gears becomes higher than 2x sidereal for only 10-100 milliseconds) TDM has realized them as GoTo movements and run self-reset and has fixed new target position. But the new target position set after this self-reset was very close (within 1 or 2 times 0.125 arc-seconds) to the previous target; so the star-image was not distorted. Only the LED-bar display (and TDM Monitor software) showed these self-resets. But avoiding even these tiny and rear situations, we applied wider moving median average filter on encoder input signal from v2.51.

- USART output signal frequency was increased from 1Hz to 10Hz when TDM interaction was switched to 5Hz (Jumper#3) previously but it did not work (USART output frequency has been remained always 1Hz). Now, this problem has been fixed; USART output runs on 1Hz if TDM interactions run 1Hz (Jumper#3 is off) and USART output runs on 10Hz if TDM interactions run 5Hz (Jumper#3 is on). Note: Jerry Hubble’s TE Monitor software is necessary to utilize this function.

- V2.51 firmware shows not just the fact of external real-time auto-guider interactions on the LED-bar display but their directions (Ra+ or Ra-) as well.

Important note: due to the fact that the above-mentioned modifications of v2.51 firmware was not carried out because of malfunction of TDM, this PIC replacement is provided just based on special customer request (but free of charge, except shipping cost).