Version 1.5 Detailed information on the Bill Of Materials (BOM). The BOM lists specific part numbers designed to fit the PC-Board. The BOM part numbers are from Digi-Key electronics. https://www.digikey.com J8: Beat amplifier gain select jumper. connect pins 1-2 for low gain or photodiode. Connect pins 2-3 for high gain. For proper operation you must connect pins 1-2 or pins 2-3. J13: beat amplifier capacitive coupling Place a jumper here when using a photodiode Some components are optional. You may not need to order all of the components on the BOM. Some components may need to be changed depending on the type of enclosure the PC-Board is mounted into. Pin header connectors: J4,5,6,8,9,10,11,12,13,14,15 These are for use with .1 inch spaced pins and cables with Dupont connectors. You can also connect wires directly to the board. Dupont cables are not listed in the BOM. These are readily available from Ebay, Amazon, Ali express etc. Oscillator: Two oscillator options are available on the board. Chose BOM components for the oscillator that you intend to use. Temperature compensated oscillator module: Use U4, C11 omit Y1,C3,C4,C8 U4, the oscillator module is not included in the BOM. These oscillators are available from Ebay, Ali express etc. Below are some links. TCXO EBay: https://www.ebay.com/itm/133439926194?_trkparms=amclksrc%3DITM%26aid%3D1110018%26algo%3DHOMESPLICE.COMPLISTINGS%26ao%3D1%26asc%3D20210609144404%26meid%3D3a1b1b8852364f948d4e4ffb8b11c6ef%26pid%3D101196%26rk%3D1%26rkt%3D12%26sd%3D384338624782%26itm%3D133439926194%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DCompVIDesktopATF2V2%26brand%3DUnbranded&_trksid=p2047675.c101196.m2219&amdata=cksum%3A1334399261943a1b1b8852364f948d4e4ffb8b11c6ef%7Cenc%3AAQAIAAABAA%252FX5kvtcYFtPo%252BGm1mGYer9jNrXTuP90gSsOB6tGLQvYNGKzQCVuC22kB6DyjNmQU2SPBERLDatutDjhqZxW6RW%252Fd1iyxjQv14oc%252BY%252BsqofUJ6mvENjhTJtW2VEUk%252BJxUR3hNRneGrlm6i1Kl5SmBKOk%252BR%252FVqk97UOLPG%252BB0XUnM5Hnu1InbbO99Og%252BvjisQMtaBF8LFx%252Fd5vlZWj9lPl6wv9EiFlj9cIgMVPPmBWGXM0LsmoOcjRiy16C%252FtNiTo%252FNk9vflPLtwFuC%252B9nMik0dmSoyYnMxtJqYN188iBkwhxY3Csrgp98zjHFu5shX9%252BlB13ZCh4cX%252Fd49F3oTbi44%253D%7Campid%3APL_CLK%7Cclp%3A2047675 https://www.ebay.com/itm/384338624782?hash=item597c5e010e:g:SewAAOxyVLNSsQdc&amdata=enc%3AAQAIAAAAwOl4MRpJTMCeTyuidFo9BwFpJc6iemRWLVrJZJRduHOeJJDQEeJiHM1bsZDuCFePv07ShXRqe7ibhpzLkF8t6hBKPeMEXImMUbNSow6MaTk7th42k2j6T01wTsDYa2y5ntsiUPj8ml65su8t3ax6tiFp1k3%2FLWuVUFG766nHBOY32AJeMBIhrwjxgFOhXzMX8Sk1ZsM2H7uc4K05Rkm5KBi%2Fp2yIAFIW3dWpvOkZc1zrRJdSq8ALZwsFqK9kLe%2FmSQ%3D%3D%7Ctkp%3ABk9SR96w_YzFYg AliExpress: https://www.aliexpress.us/item/3256803010852087.html?spm=a2g0o.detail.100009.5.285cYn4DYn4DDU&gps-id=pcDetailLeftTopSell&scm=1007.13482.271138.0&scm_id=1007.13482.271138.0&scm-url=1007.13482.271138.0&pvid=9f95260a-2212-400e-a9d8-4b548e0cab6a&_t=gps-id%3ApcDetailLeftTopSell%2Cscm-url%3A1007.13482.271138.0%2Cpvid%3A9f95260a-2212-400e-a9d8-4b548e0cab6a%2Ctpp_buckets%3A668%232846%238108%231977&pdp_npi=4%40dis%21USD%218.18%218.18%21%21%2159.35%21%21%402101c5ac16929022010112093e7905%2112000024613733531%21rec%21US%21%21A&gatewayAdapt=glo2usa https://www.aliexpress.us/item/3256802600223853.html?spm=a2g0o.productlist.main.5.fcae5345IwPYs9&algo_pvid=597995d0-3475-4a0b-8adf-f033a6a46281&algo_exp_id=597995d0-3475-4a0b-8adf-f033a6a46281-2&pdp_npi=4%40dis%21USD%2117.50%2117.5%21%21%2117.50%21%21%402101d64d16929020656294441eb1f5%2112000022181717924%21sea%21US%211695734699%21&curPageLogUid=u3CG3MIlODV4 Crystal oscillator: Use Y1,C3,C4,C8 omit C11,U4 C8 is used to adjust the oscillator frequency. A precision frequency reference is needed to do this. I use a frequency counter connected to a GPSDO. If this equipment is not available, C8, the trim capacitor will be useless. In this case, I would suggest that you omit C8 replace C3,C4 with 18pF capacitors. or, if a different crystal is used replace C3,C4 with the recommended load capacitance for the selected crystal. Also, I have an an 18pF crystal installed but actually needed more than 18pF to trim the crystal. You will very likely need to adjust these capacitor values to match your crystal. Pushbutton switches LED's and potentiometer: SW1-SW4, R11, D1,D2 These components are for mounting the board under the top of an enclosure. Switches and pot go through holes in the enclosure. You may need to use different components if you use a different mounting method for the board. Jacks J1-J3,J7: The same applies here. You may need to use different jacks and mount them off board depending upon the board mounting. These were designed to go through holes in the side of the enclosure. Parts not listed in the BOM: U2 20 pin IC Socket U3 8 pin IC Socket U4 TCXO oscillator module Jumper cables with Dupont connectors. Clock beat sensors: Temperature sensor: See https://mesterhome.com/timer/Sensors.html on this web site. LCD display with I2C adapter: Bluetooth or serial adapter: See https://mesterhome.com/timer/Construction.html on this web site. 9VDC power adapter: Batteries and battery holder: Optional battery backed clock: See https://mesterhome.com/timer/pcboard.html on this web site.