PA Chime Generator: Difference between revisions
Matt Parnell (talk | contribs) Created page with "Upon replacement of the audio system in 2020, some individuals remarked that they missed the four-tone chime of the prior system. == Background == The prior PA unit was an I..." |
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The schematic in the [https://www.arstel.com/catalog/public/pdf/service-manual/PA-9100RC_9200RC.pdf PA-9100RC/9200RC Service Manual] shows that the chime tone is generated by IC101, a BXA4240. No datasheet could be found for this part. Fortunately, a datasheet for a pin-compatible equivalent (the IK Semiconductor BT8040N) has been found [http://pdf.datasheet.live/83efda62/bms.by/BT8040N.pdf here]. | The schematic in the [https://www.arstel.com/catalog/public/pdf/service-manual/PA-9100RC_9200RC.pdf PA-9100RC/9200RC Service Manual] shows that the chime tone is generated by IC101, a BXA4240. No datasheet could be found for this part. Fortunately, a datasheet for a pin-compatible equivalent (the IK Semiconductor BT8040N) has been found [http://pdf.datasheet.live/83efda62/bms.by/BT8040N.pdf here]. | ||
The BT8040 is a "melody generator with accompaniment". Some key observations: | |||
* The resistor-capacitor (RC) circuits attached to ENV1 and ENV2 likely provide audible decay (envelope) of the the tones. In the PA-9100RC, each consists of a 4.7 uF (50 V) electrolytic capacitor and 100 kohm resistor. These same values will be used in the new design. | |||
* The SEL1 pin (#6) is pulled HIGH (to VDD) while SEL2 (#5) is left floating (LOW?). This appears to select the "do-mi-sol-do" melody, according to the BT8040N datasheet. This is consistent with a spectral/audible analysis of the PA-9100RC. | |||
* It's not clear whether the musical key is affected by the 1 Megaohm resistor between OSC1 and OSC2, or if this just sets the speed (tempo). According to the BT8040N datasheet, this resistor can span from 500 kohm to 1.5 Megaohm. 1 Megaohm will be used to match the PA-9100RC. | |||
* The MT pin (#4) is used to trigger the tone sequence. | |||
* The driver circuit (P1, OUT1 and OUT2) is not used. | |||
* Audio is provided via the MO pin (#12). In the PA-9100RC circuit, there is AC coupling (C1), an application of DC bias (R1/R2?). The purpose of D1 is not yet understood. This circuit will require further analysis. | |||
== Project Status == | == Project Status == | ||